I started Eschaton Books back in 1993, as a side project for publishing my poetry back when I was still a VP in a PR firm. At the time it just looked most cost effective (plus, you got the full run of a number sequence, from 000 to 999) for me to buy 1,000 ISBNs, so I did.
Of course, back then, I used a couple of dozen and the rest had been loitering around in whatever digital void that these sorts of thing do until I resurrected Eschaton in 2008-9 to do the books for Simuality's Avatrait gallery, and then again in 2014 when I started doing the big poetry books, and, subsequently, the book review books.
Now, 1993 is a very long time ago - almost a quarter century - and in the intervening years, the US registrar for ISBNs, R.R. Bowker (predictably) moved into computer systems, and on-line ways of updating one's registration files. Which I, naturally enough, didn't really have a clue about until relatively recently. Anyway, I spent a good chunk of the afternoon updating (I guess Amazon must feed data to them, as most of my review books had most of the info - including cover images - in place) the files for at least my review books.
I sort of hit the wall, however, when I got around to the poetry books. I had been sort of a "bad boy" when it came to these as I basically just re-assigned the ISBNs from the initial "saddle stitched" "chapbook" editions of the small collections, as well as those that had been assigned (back in the day, you mailed in paperwork to the Library of Congress) to the annual collections (which had originally come out in hand-xeroxed editions of 12 that were then comb-bound with grey Classic Laid cardstock covers). It's typically "bad form" to re-use ISBNs, but with the sole exception of my last chapbook, 1996's "Some Semblance of Decay", none of them had the ISBN anywhere IN the books, and that only had it with the barcode (it was also the only one of those with a barcode). So, I guess it's going to be another "hanging over my head" project to get the info on the Bowker site for my 20-some-odd poetry editions in line with the current into.
However, tonight I'm going over to Starbucks to write reviews.