Subversion was (to my surprise) only released in 2000, so you'd have to migrate from something even older -- perhaps CVS (released in 1990)? RCS was released in 1982, so you might have migrated from that. SCCS was released in 1972, so they MIGHT have used it, and kept those migrations going. But my guess is they fudged the git history as some weird type of historical documentation of where these languages came from?

My oldest photo in Google Photos is from 1994.

My oldest email in Gmail is from 1996.

My oldest file in Google Drive is from 1998.

All of which pre-date their current storage (and some of which pre-date the company that created the current storage).

None of which is as important as anything in a VCS in terms of wanting to keep history intact.

BTW: If any Google engineer is present: Gmail search over mail older than a decade is terrible. Just terrible.

Well, if it was migrated to Subversion from CVS on the day Subversion came out, that gets us back to 2000.

If it was migrated to CVS from RCS on the day CVS was released, that gets us back to 1986.

If it was migrated to RCS from SCCS on the day RCS came out, that gets us back to 1982.

SCCS showed up in 1972, just in time for this commit.