Well, so far what I can gather is that the FAD movies are the oldest. And that FAX movies are just re-releases of FAD movies.Returning to the codes for a moment, you'll find FAD code releases not only in line with FAX but also with others. Here are a couple of examples from my レズ collection:
FAX-440 = FAD-1597
DTRS-036 = FAD-2230
HQIS-058 = FAD-2260
HTMS-028 = FAD-1966
Try copying a link for a cover for one and doing an image search with Google Images or Yandex and you'll probably find both equivalents.
There are some other tie-ins such as covers showing both FAX- and just X- using the same number.
The same thing also occurs for FABS- and FABR- where I'm pretty confident these stand for (S)ale and (R)ental. A rental prefix or suffix happens routinely with many other studios. Many of these covers will even show "for sale" or "rental only" in English on them.
Also, sale and rental is one thing, but here's what I want to know - how far back in time do Henry Tsukamoto movies go ?? And which old stuff is available on the internet. I ask this because of the AOFR movies, even on JAVLIBRARY it says that they were released after 2011, which leads me to think that they are also re-releases of HENRY's older movies, because as per the video quality they seem like they were shot before 2000 something.
Recently I came across a video on Youtube where TOORU OZAWA is talking about how he has completed 40 years in the industry, so that means that he started working in 1984! and he says that he was doing it before AV was AV and I find it really fascinating when he mentions that "it starts and ends with HENRY's work" :-
And it is clear that even these veteran actors look at HENRY TSUKAMOTO in a completly different light altogether :-