From ISFDB

Work-in-progress...

Unless otherwise stated, these refer to ASINs for ebooks, not ASINs on physical books (which historically were the same as the ISBN-10, but IIRC aren't for 979 ISBNs).

The following are cases where ASINs may not be as straightforward as they seem...

International publication with different ASINs in different territories

Some publishers - e.g. Solaris, Angry Robot, Titan Books, Tor.com - operate internationally and publish editions for all English-language markets. (This doesn't apply to all their output, e.g. Titan publish US versions of some books that Gollancz originally published in the UK; Angry Robot publish UK editions of Kameron Hurley books that Saga Press do in the US, etc. But I digress...)

In some cases - definitely Titan - the same ebook uses different ASINs in the Amazon.com and Amazon UK stores. Ideally, both of these should be recorded in ISFDB, with the pub note indicating which ASINs apply to which store(s). (It's unclear why some publishers do this and some don't - maybe related to their internal systems?)

Grey/grey imports being superceded by official local releases

If a title has only been acquired for a publisher for a local market, it may still be available on Amazon in other regions as a gr[ae]y import. This isn't always the case - e.g. the Gollancz-published UK ebooks of Paul McAuley are on Amazon US, but the Head of Zeus published books of Adrian Tchaikovsky aren't.

Things get complicated if a local publisher subsequently picks the title up for an official release. In such cases, it seems Amazon serves an error page for the original gr[ae]y import. Example: James Bradley's Ghost Species original Australian ebook, later UK ebook

Non-local Amazon serving local ebook

If you visit the ebook product page on an Amazon site for another country, but the title has an official ebook release in your local territory, you will (probably?) be served the details for the latter, even if you specified the ASIN for the former in the page URL.

e.g. if you visit Amazon US from the UK for Cory Doctorow's Radicalized using the US ASIN B07HWY7XG8, you'll be served a page for the UK pub with the ASIN B07GBDFW4W. The page's URL will still likely refer to the US ASIN (example), but if you scroll down, you'll see the product details show the UK publisher and ASIN.

If you visit an Amazon site from a third country, then things become even less predictable. Basically, if getting ASINs from a non-local Amazon and/or for a non-locally published title, try to get some other verification that you have the right value e.g. from Goodreads.