OK, first of all, thanks for the quick reply.
Now, i've added the Leonidas Class as you've advised me to do so. I updated my personnel files via SH3Cmdr but i didn't see any change ; it still shows us M02X. But this maybe due to the way SH3Cmdr works. It is probable that it will be displayed correctly next time i sink a M02X. I've gone through the listings of English Names.cfg. There is no other identical entry. Is there any other .cfg file i should check?
P.S. It is not a big deal if a type of ship doesn't show up correctly. Sorry to bother you. I was just curious to find out what happened. Too many mods, too many files altered. Sometimes it is easy to get carried away and mess (hopefully only) a few things up. I'm too tired to wait for the museum to load right now but i will check if it shows up correctly there, tomorrow. It is 02.16am here... Thanks, mate.