The Evil Dead/Evil Dead II Connection

DISCLAIMER: this theory was developed many years ago, long before the TV series would be released. It's just a theory based on the assumption the first 2 Evil Dead movies happened in two different times, at different locations.

Premise: there are two different cabins, TED (Morristown, Tennessee) and ED2 (Wadesboro, North-Carolina). There are two different Books of the Dead, two girls named Linda. There's a gap of eight fictional years in between the events depicted in the movies.

1970s: the first (unnamed) archeologist discovers the infamous Naturan Demanto, a demonic and sentient copy of the original Necronomicon, in the Kandar Castle. He brings the book and its accompanying Soul Dagger in the States, rents a cheap cabin in Morristown (Tennessee) and translates the incantations. The Kandarian Demon possesses his (unnamed) wife and he is forced to dismember her. Then, the archeologist, scared and weak, drives away from the place in order to save his tainted soul but he accidentally dies (remember the car stuck in the swamp mud you can see at the very beginning of TED, during the opening titles?!). The Evil Dead's license to possess beings expires; however the presence and influence of the Kandarian Demon in those woods has been firmly established.

1979: many years later, Ashley J. Williams, his sister Cheryl (gifted with ESP power), his girlfriend Linda and his friends Scott & Shelly rent the same cabin and inadvertedly unleash the Kandarian Demon. 'THE EVIL DEAD' happens. The Naturan Demanto is finally destroyed by Ashley. Now the Kandarian Demon has a limited time to survive in the living world, since the specific incantations from the Naturan Demanto bound it to the physical existence of the book. It attacks Ashley (the ending of TED), before vanishing forever (during the final credits). Ashley, barely alive and severely wounded, walks along the alternative trail... he is later rescued by some people down the road. He doesn't remember anything and looks traumatized/psychotic.

1980: the events of Morristown are investigated. At first, Ashley is erroneously believed a serial-killer. Then, Police hypothesizes outside individuals must have murdered Linda, Cheryl, Scott and Shelly. Corpses have been mysteriously incinerated by some strange and unidentified acid anyway. The unsolved case is archived under the codename "The Dismemberment of Morristown". Many urban legends surround the story in the following years (food for fan fiction). 

1980s: post-traumatic stress and minimal brain damage have made Ash forget everything about the Kandarian Demon. He is internalized into a psychiatric hospital for years. Apparently, he is cured, albeit still amnesiac about the events which wiped out his sister and best friends. In the process, he got more muscular, skilled and confident. Once dropped his engineering studies at the Michigan University, the guy finds a job as clerk for the local S-Mart store. He meets another girl named Linda, who soon becomes his new girlfriend. Subconsciously, he is attracted by "this" Linda for his past and unsolved involvement with TED Linda. On the other hand, the two fall in love for good and swear to be "always together".

In this same time period, Ash is given back his 1973 Oldsmobile Delta 88, once left abandoned in Morristown. Ash believes this car is one of the missing links to unveil the Morristown event.

1986: the second archeologist, Dr. Raymond Knowby, finds a secret rear chamber in the Kandar Castle where the original Necronomicon Ex Mortes a.k.a. Naturum Demonto and a bigger Soul Dagger have been stored for six centuries... on six years since the first archeologist discovered the Naturan Demanto volume preserved into another chamber of the same castle. Knowby is supported by his wife Henrietta, his daughter Annie and associate Professor Ed Getley. Part of Knowby's work is based on the TED archeologist's account and academic studies. Knowby has even found a way to retrieve his old Panasonic Solid State RQ-706s tape recorder.

September 1987: Knowby comes back to the States with the book. He and his wife Henrietta retire in their own old family cabin in Wadesboro, North-Carolina. The archeologist translates the incantations of the Necronomicon, and a more powerful manifestation of the Kandarian Demon raises once again. Knowby kills his possessed wife and buries her in the cellar floor. Then, he accidentally dies and his soul is "absorbed" into the outerdimension, the Dead World. 

October 1987: Ash decides to buy a cabin and thus dig out his unconscious and tormenting reminiscences. His superhuman empathy with the Book of the Dead and the Kandarian Demon is fully active and brings him on the "right path". He and Linda go to Wadesboro to meet the Knowbys which, in hope to sell their cabin, many years before had placed an ad somewhere. Without the Knowbys around, Ash and Linda sneak in the cabin nonetheless. EVIL DEAD II: DEAD BY DAWN happens. Ash is soon joined by Annie Knowby, Ed Getley, Jake and Bobbie Jo.

Notes:

1- Ash inherited the same ESP power her sister Cheryl displays in the first part of the movie. See the "sketching the Naturan Demanto cover out of nowhere" sequence in TED or the "I feel like someone is walking upon my grave" sequence in ED2. The two siblings have a spontaneous spiritual tune-up/empathy with the demon and the overall supernatural world.

Most importantly, since the Predestination Paradox rules upon the Evil Dead universe (whose timeline is fixed and immutable), Ash and the Kandarian Demon "already" have a long story battling each other in the ancient ages. Do not think linear when dealing with time-travelling...
By the time the events of ED2 are about to occur, Ash is indeed subconsciously "sensing" the Necronomicon.
Ash's psychic powers are confirmed in AvED Episode 4.

2- The silver necklace in ED2 was the same of TED. Ash obviously gave the necklace to ED2 Linda prior to the events of ED2. He was just "faking" he didn't know what it was, must be a running gag between the couple; it was evident from Bruce and Denise's acting. Ash: "Hey... what's that?" (knowing look in the eyes and big smile, like he was saying: "Well, this is my gift, you are wearing it and you're happy, isn't it? I'm a God").
 

3- Presumibly, as showed in the ED2 deleted scene, Ash incinerated the Necronomicon Ex Mortes, hoping that move would stop the Kandarian Demon like it did in Morristown. It didn't work as planned anyway.

4- In TED Ashley must have deleted all tape recordings of the archeologist in order to not make them found by anyone else. He could have done that right after he listened the last entry on how to stop the Deadites. In AvED Episode 10, the Evil Dead mystically "digs out" the old recording from the tape, despite Ash had wiped it out in 1979.

5- As depicted in the movie, ED2 Linda raised from the ground (where Ash buried her) and started dancing, wherever TED Linda had been left unburied after the decapitation... plus, TED Linda wasn't a dancer and never attempted to dance either as human and Deadite. 

6- Ash checked out the bridge in ED2 because he didn't know it had been sabotaged by the Kandarian Demon.

7- In TED, the rifle was single-barred. In ED2, the rifle was a double-barred Remington whose specific model is even sold at the S-Mart store (Ash II in AoD wasn't implying that the "Boomstick" was coming from the store). Notice that in ED2, Ash "produced" two holes in the main door by shooting at Annie, Ed, Jake and Bobbie Jo.