I wish I had a full changelog for GameEx all in one page... I know there were a couple times we had to update GameEx because MAME broke the xml structure, and I know there was a pretty major update right around GameEx 14.82 (or maybe it was 14.83).
I'm trying to find the update we did for MAME compatibility, since your old GX version may not play nice with MAME 0.198. I'll let you know when I find it, because if you can't get MAME to help generate a proper GameList, that's your problem right there. And MAME's -listxml would certainly be a problem if GameEx isn't able to parse it.