Maybe the first part of Mulholland Drive is not really a dream of Diane's, but one of the movies Diane and Camilla starred in together. The dinner party would then be a post-production wrap-up party, and Adam would just be an actor and not a director — which explains why we find all the same actors from the first part, under different names. That is all about cinema: the same people, under different identities, playing written roles. — HarryTuttle
Maybe the first part is not just a "documentary" about the movie they shot but an altered recollection of memories from this movie by Diane in her dream — a confusion of personality between Diane's roles and her identity. Some hints:
- Adam never states his job in the reality part.
- Only Coco is presented as Adam's mother. Maybe Diane only knew her professionally on the set, but never got the opportunity to talk to her personally, and didn't know Coco was Adam's mother.
- The party looks like a production wrap-up party, maybe on location. Camilla gives her the address because Diane never worked on the set of 6980 Mulholland Drive.
- That explains why they wait up for Diane for the dinner — she was Camilla's supporting actress.
- At the party we have the following characters from the "dream" part: Camilla as Rita, Diane as Betty Elms, Adam Kesher as Adam, Coco Lenoix as Coco, Badalamenti as Luigi Castigliane, blonde kisser as blonde Camilla Rhodes, the Cowboy as himself. Wilkins? Where is Wilkins?
- Maybe this film was a mess for Camilla and Diane — they had an intimate relationship during the shooting, but Camilla went out with Adam (the lead actor) in the end.
- The Sierra Bonita apartment "looks" the same in the film and the reality where Diane lives in the end. Could be distorted dream recollection, or just a different place.