Was trying this out, but it is not bringing some details I would have expected.
For example, I added John D MacDonald and set the amazon author url to
https://www.amazon.com/stores/John-D...hor/B000AQ52CK
When I check for missing books it only brings up one book.
If I use Apple (by unticking the amazon exclusive box), then it brings the same book up along with 13 others including this one
https://books.apple.com/us/book/the-...er/id887496700
But that book is also on amazon and under the correct author name see
https://www.amazon.com/stores/author...2-5fdd68033b69
Why doesn't it appear when using amazon?
Another minor issue is - if I use the 'Get Books' option on any of the books that do appear, it doesn't just find that book, but lots of false positives. (I realise that may not be your fault as the 'Get Books' filtering does not make sense to me, but perhaps you can find a way around this issue)