I did a back of an envelope exercise a few months ago, putting together the 164A's we know about on here, plus those sold at LCA and other known auctions, plus those in well known collections. It came to about 23. So you could perhaps reasonably assume there are say 60 +/- 10, extant in total worldwide. Something like that.
So when I said not too wide of the mark, I meant by comparison with some of the other estimates, not that it was a truly accurate representation !
As you say the 1922 trident dot is no doubt an under estimate as well.