Your last part is not correct. We had the "old-gcc" RCS files, it just was in a format not parseable by CVS. It was not entirely lost, just not easily accessible. Ian Taylor went to the trouble of rewriting the RCS files CVS had, and that we based the SVN repository on, to include the old data, so actually, SVN had more history than the CVS versions, dating back to 1987.
EDIT: Apparently all previous history was lost when they implemented CVS, circa 1997. We could always ask someone in the oldest maintainers file available (https://gcc.gnu.org/viewcvs/gcc/trunk/MAINTAINERS?revision=1...) and have the real answer.