I contacted Alexey Popovsky, the owner of Rusbase, to ask how many games he has in his online archives. First he informed me that the site had moved to a new address...
...and then mentioned that it contained 'about 60.000 games'. I counted the number of events on the newer site and came up with 2456 events instead of the 2442 events mentioned in my post Rusbase, as counted on the older site. The other numbers I reported in that first post and in the follow-up post Events Covered by Rusbase are close enough for my purposes.
Rusbase is a wonderful piece of work. It's a pity that there is no equivalent USAbase.