Well, I have not noticed such a thing with other adult videos in the past. I turned the disc over and inside of the center hole, besides the title of the disc (which you have to turn a certain way to the light in order to see the writing), the only thing that I could see that might indicate the manufacturer of the disc, was 'LMW/CA'. Other than that, on the face side of the disc, after a whole bunch of 'Production Dates', it then lists a single 'Duplication Date'.
Your comment about
"Cybervision and Entvideo is like that also. Consequently hitting a button could take you somewheres that the owners manual has no explanation for."
reminded me that I have several times experienced unwanted 'functionalities' using this APEX DVD player & remote combo. Like switching between the use of the 'step', 'slow', 'fast/rev forward' and 'A-B' buttons or other buttons on the remote, has sometimes completely 'dropped' me out of the selected 'scene' entirely, and I found myself back at the beginning of the disc or somewhere like that!
However, perhaps such 'extensive' use of the remote buttons might cause any remote to 'hang up' and not be able to follow the desired sequence of button use fast enough!
This, of course, usually happens only on 'Farscape' and 'Babylon 5' DVD's, when you are attempting to follow the 'Bad Guys' when they go into 'warp-space-drive'! (Yeah! S-u-r-e!)