Regular 1985 Bill would still know Calvin Klein and a strange old man with an odd sports almanac.
That and 1985 Biff did see a flying car right out in public in broad daylight.
So technically Marty and Doc didnt "fix" 1955
They fixed it enough.
1955 Biff didn't have the almanac, so couldn't make any bets. The fact that he saw Calvin Klein and a random guy steal it off him doesn't really matter. He can't make any bets, and can't become rich.
He does know now that there's some guy out there with a flying car, but what can he really do about that information? Nobody would believe him if he told anybody.
The only thing that really changes is the in 1985, Biff sees a flying DeLorean. Even by Biff's standards, it'd be possible to put 2 and 2 together. Or at the very least, work out that the flying car in 1955 and the one in 1985 were linked somehow. But again, he can't really do anything about it. Marty and Doc went into the future, returned to a different version of 1985, returned to 1955, went to 1885, then Marty returned the time machine to 1985 where it was instantly destroyed. Even if 1985 Biff worked out that there was a time machine, there was never a point where he was able to get his hands on it and use it. And again, without any proof that the flying car exists, there's nothing he can really do with the information.
You are right. Biff couldn't make any bets so nothing would change in the 1955 timeline. However in the time following the events where Biff loses the almanac I am sure he would think real long and hard about the whole thing. A mysterious old man who knows a little too much about him shows up out of the blue to give him a book a sports almanac that he proved could make him rich, and then his newfound rival at school Calvin Klein steals his book, and escapes in a flying car. Biff would start pondering the old man's words even more now. Especially the (one day a crazy wild eyed scientist, or a kid would come asking about that book comment) That being said this might affect the demeanor of 1985 Biff quite a bit. Originally he was just humbled by George Mcfly knocking him out, but to know you had a gold mine in your hand, and blew it might lead to serious anger issues, and over time suppressed rage.
Biff would never forget about Calvin Klein, the mysterious old man, the almanac, and the flying car from that point. He would be haunted by it forever. He would later realize Marty Mcfly looks just like Calvin Klein, also Marty happens to hang out with a crazy wild eyed scientist. He might also notice that the older he gets the more he resembles the mysterious old man. Big goofy, pussy, whipped Biff could have a moment of clarity where all the pieces would come together. That point would be Marty showing at the end of the movie donning the Cowboy outfit. Which is another thing that subconsciously associates Marty with time travel.
A few scenarios could happen at this point. Biff's memory really has faded and he simply dismisses it all as nonsense. 2. He flies into a fit of rage, gets a gun, and guns down Marty, and possibly his whole family. 3. Biff starts to think even more, and decides to play the long game. He watches Marty more carefully, spies on him, follows him around. His endgame goal being to catch Marty meeting with the Doc again so he can once again gain access...
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to the time machine, and fly back to 1955 to thoroughly warn his younger self about Marty, Doc, the time machine, and the fact he must hide that sports almanac in the most secure place for the next 3 years. Also If I was Marty I would be smart enough to realize after returning from 1885 that Biff was a potential liability, and I would either be watching him like a hawk, or just decide to get the hell out of town.
share"decides to play the long game. He watches Marty more carefully"
I think thats fairly likely , perhaps thats why he volunteers to wash Georges car etc.
So theres a good chance Biff was watching the inititial experimernt in the car park wioth the libyans ...
..but Marty (nor doc) could be watching him like a hawk as they dont yet know the influence they've had on Biff's life