I have a PB copy of 'Where the Crawdads Sing' and the ISBN is not found by PBS though there are many, many other versions both in PB and HC. I see 3 other members have posted the same book 'without an ISBN' so I am assuming I would have to do the same and probably never get my copy requested. Am I right to think I should just pass on to my FoL bookstore?

If it has an ISBN I would search that a few more times. It's possible it might take a few days for the sytem to find and sync. I've usually posted all my books regardless of how many copies with or without ISBNs. Someone searching your shelf might want to get it and even short ISBNs do get requested eventually. I searched for paperbacks and along with all versions of that title and it looks like there may be less than a dozen copies posted all together; it might be worth it to put on your shelf for a while.

Thanks, Linda, I usually post even when there are dozens of copies already posted.