For what is worth I understood your meaning immediately by applying the "most generous interpretation" principle.
Might I suggest phrasing it exactly like that then? “I resigned all 12 positions I held at Apache because X” is a lot clearer to me.
1/ because I don’t remember exactly how many,
2/ because the record keeping at Apache was so haphazard at the time, half of the places I resigned from left me on the roster anyway (like the HTTPd server project itself).
or even further, naming some of the relevant positions (for example HTTP Server project management committee)