"Used to hold" screenings doesn't mean you're compelled to go. Or watch the screener. At least one voter openly said they didn't watch the movie back then.
If you don't see all the nominees, you shouldn't be able to vote. But that's only my opinion. It's like me saying I had the best sushi in...
That's an argument that has been around for years and theory that was openly acknowledged with Brokeback Mountain/Crash in the run up to that Oscar telecast.
The original comment was that BR has no chance of winning Best Picture because of Bryan Singer. My contention and argument is that it does have a chance at the Oscar regardless of Singer because it has already won a BP award at the Globes.