How many HP35s with The Bug are still extant?

I bought my HP35 in 1972, one of the first HP35s made. It has The Bug, that is, it says that antilog of 1/2 [log of (1.01) squared] = 1. My husband's HP35, bought a month or so later does not have The Bug.

I still routinely use my HP35. Ergonomically, it is superb and unlike newer models, it is not cluttered with (what I consider to be) marginally useful functions.

My question is: How rare is a working HP35 with The Bug? Does anyone even know? Is there any data to estimate the answer to this Q? I have no plans to sell mine, ever, so this is not a question prompted by dollar signs.

Vintage Calculators Web Museum says my HP is rare, but gives no estimate of how rare.