I havent set my mind to anything, you're simply not reading what i'm saying. Of course a cinavia enabled player won't reject older discs, they'll only refuse to play backup copies that carry the signal and thats post-feb 1st. Refusing to play "old" discs would be like a 2015 player refusing to play 2014 discs. Part of the standard is ensuring backwards compatibility if they want the player licensed.
How is it that years back companies that were going to use Cinavia (maybe) in the future would put data in the discs they made to ensure no copies would pass muster and be played using Cinavia?
Sorry, that line makes no sense at all. They haven't put "data" in it that cause them not to be played.
Understanding how cinavia works is relatively simple. An inaudible signal is added to the master copy of a movie, cinavia checks if the disc is encrypted, if it is, everything is peachy. If it isn't it will require the player to mute the signal. Play a cinavia infected backup disc in a 2012+ player => it will mute the audio, play it in a 2011 or earlier player, it will play just fine. For the simple reason those models pre-date the mandatory detection date and lack the needed hardware to detect the signal.
Originals (cinavia or not) will play just fine in post 2012 player. Cinavia could care less about originals. It's a DRM to prevent the playback of BACKUP copies that have been decrypted. It works like this: insert a cinavia infected backup disc, player checks for cinavia, cinavia is found, cinavia checks for disc encryption (AACS, BD+,... which obviously arent present because its a backup), cinavia sees no encryption, cinavia then tells the player "hey, thats an illegal copy. Stop the audio immediately and display message X".) Cinavia only comes into play when you want to play backups on a 2012 or later cinavia enabled player. Play an original, you've got nothing to worry about. When those originals were produced (2012 or before) is irrelevant, WHEN only again comes into play for backups to decide wether there's a chance at them having cinavia on it or not.
New BDs and some DVDs have something triggering the Cinavia audio block, and will older or non-Cinavia detection mark-imprinted BDs and DVDs always play in Cinavia enabled players, now or in a few years?
Of course they do, thats the essence of cinavia. The inaudible audio signal inside the movie audio track, that signal itself IS cinavia.
Do all older non-marked BDs and DVDs get a pass from newer Cinavia enabled players forever?
If the discs don't have cinavia on them (and only a handful of studios use it atm due to licensing cost), if they're original ones the player is gonna play them just fine. Again, cinavia only comes into play for BACKUP DISCS that are unprotected.
If not, how does an older disc (or copy) get to play in a new player?
No such issue. Part of the standard is ensuring backwards compatibility, new players won't refuse playback of old discs. In fact it would sooner be the OPPOSITE where OLD players would refuse to play NEW discs due to changes in the BD standard technology and the player (or its firmware) no longer knows how to handle them. Even that is highly unlikely, My old DMP-BD85 still plays new discs just peachy.
Seems like if an older valid BD can play (or a copy) in a Cinavia Bluray Player undetected there is a special backdoor for older presses of DVDs and BDs.
There are no "backdoors". The disc either has cinavia or it doesn't. If it has, then the original versus backup comes into play.
cinavia + original disc + cinavia enabled player: no problem whatsoever
cinavia + original disc + pre-feb 1st 2012 licensed player: no problem whatsoever, player lacks the technology to detect the signal
cinavia + backup disc + cinavia enabled player : Cinavia will kick in unless the signal is removed from the backup
cinavia + backup disc + pre-feb 1st 2012 licensed player: no problem whatsoever.