Ok nobody is paranoid enough or you don't admit that you are.
I've done some internet search over the week end and here are my "as good as gets (c) solutions" :
There is a small and excellent tool mp3utility that checks a folder of mp3 files. It create two text files:
1) list of errors on mp3 files
2) a tab deliminated database of file features (tags + technical info such as number of frames) that can be directly exported to excel
You can create log files for both the errors and the info files and you can compare these logs. Although that does not verify that the sound part of the mp3 file has not changed, in effect it checks that it did not get corrupted or replaced by another mp3 file.
I recommend opening the info log in excel and removing some of the columns such as date that are expected to change often and save it as a tab delimited text file, and replace all tabs with paragraph marks before comparison because otherwise most comparison programs will mark the whole file info as change rather than the changed attribute only.
Something similar to file 2 can also be created using MJ (select all files, copy, paste to a text file). If you make a fresh scan of the recent files and backups with MJ, you can compare the results.
You can use a similar technique if you wonder about the difference of the MJ database file and the information that reside on files. Just compare MJ, to a fresh MJ Scan.
These all take a long time, but the manual work is not very much and I plan to do this every month or so when I replace the backup database with the most recent one.
Does anyone have better ideas on comparing two MP3 databases? For example comparing 2 MJ Databases?