(Much snippage, so apologies if the attributions have gone bonkers)
"Get fed up tripping over them" would be an exaggeration, but there are certainly individual regions, towns, and even homes which have a concentration much higher than "average", while there are others where none will be found. (The same can also be said of anglos.)
My own personal "guesstimate" is that the number 546 is far too low.
More than once I, or rather my Wheatstone, has been one of 5 or 6 ECs in the session at the Crown in Worthington a few miles north of Bolton. I would be astonished to learn that that one session would represent 1/100th of all the active concertinas in England, especially as I personally know at least 5 or 6 other EC players as well. Am I really on first-name terms with 1/50th of the EC population of England? Doesn't sound likely to me
Don't get me wrong, I'm not having a dig, I'm thinking out the likelyhood of the maths.
Anyone know if the ICA have any figures on geographic spread correlated with concertina type? That would be a partial estimate (I for one am not a member of the ICA) but it would perhaps get us slightly closer to an estimate ...
And if anyone really is fed up with tripping over a decent loud steel-ended 56-key EC (not accordeon reeded), I'll happily move it out of your way at no charge whatsoever and give it a very good home