This problem seems to be a worldwide problem, because the date "1970-01-01" is the start of the UNIX time. UNIX datetime values before this point in time are negative.
There are still applications out there in the world, which do not support negative UNIX time.
Mp3tag does not support negative values for the raw datetime variable %_file_mod_datetime_raw%.
"-476038800" should point to datetime "1954-12-01 07:00:00".
Total Commander can set modified datetime into the past before "1970-01-01".
Yes, that will stay that way. I doubt that you had any access to computer facilities in 1954, and if so, the MP3 format became a standard not before 1991.
So, unless you misuse the "modified" date, it is not possible to have digital mp3 audio files with a modification date before 1982 (the start of the development).
And even if you take the PCM method for audio files, then the first recording was available in 1971 - well after the 1.1.1970
If you want to record the releasedate of a recording then use the field YEAR or RELEASETIME.
The solution to my problem came in form of FileDate Changer, a piece of software by Nir Sofer
I allows me to manipulate the date and time of modification of files [and also creation and access]. And by choosing a false modification date like 2000 02 02 00:00, I will be easily able to distinguish certain special files from others