Revealing mistake: When the eye is flying toward Bobby Jo, you can see the rig holding the eye as it flies and the wire when it enters her mouth. (00:41:45)
Revealing mistake: During the scene when the evil Henrietta flies up from the basement to attack the girl, while she is in the air you can see the wire holding her up, a split in the butt of the latex costume and as she turns to see Ash, sweat pours out her ear. (01:11:20)
Revealing mistake: During the scene in the tool shed in which Ash mounts the chainsaw to his arm, you can see duct tape holding the chain bar on the chainsaw; this wouldn't exist if he'd just mounted a chainsaw onto his arm.
Revealing mistake: During Ash's fistfight with Henrietta near the end, the blade of the chainsaw can be seen flopping like rubber. (01:12:10)
Revealing mistake: Evil Ash has no hand (just a stump) however when he grabs Annie and throws her into the wall, he has his right hand back. (01:01:10)
Revealing mistake: After Ash is punched unconcious by Jake, as Annie shakes him, screaming at him, he grabs her arm, although he's out cold. (00:36:25)
Revealing mistake: When Ash is fighting the headless corpse in the shed, in one shot the chainsaw bends clearly. (00:20:10)
Revealing mistake: Ash faces the oval, wall-mounted mirror and tries to reassure himself that he's fine, until his mirror-image lunges out and tries to strangle him. Throughout this scene, the background set and lighting "reflected" in the mirror changes very noticeably between the real mirror and the hole-in-the-wall practical effect. Additionally, the Ash that lunges through the mirror is NOT a "mirror-image" of the other Ash, as the blood patterns on their faces are distinctly different, which is obvious in the face-to-face profile shot. For that matter, the blood patterns on Ash's face are inconsistent all throughout the film, frequently from one shot to the next.
Revealing mistake: When Evil Ed tears off some of Bobby Jo's hair and eats it, the head is made out of latex (Watch for how easily everything bends on his face, even the jawbone bends at one point).
Revealing mistake: When Ash stomps the trapdoor onto Henrietta's head and her eye flies out, the closeup reveals that the "eye" is something like a styrofoam ball with the veins painted on.
Revealing mistake: As Ash is duct-taping his sleeve shut after he cuts off his hand, you can see the impression of his largest knuckles and first two fingers under the cloth. (00:31:45)
Answer: Sam Rami could not get the footage of Evil Dead to use in the sequel, so he remade the movie in a shortened form for the beginning. Since Linda was the only original character other than Ash to come back he included her in the recap but deleted the others as not to waste time. An in universe answer could be that trauma of losing his friends made Ash block them out and rewrite history in his head, except for Linda who comes back to haunt him in the movie so he is forced to deal with it.