I just noticed this morning when I went to check about this week's free Wordsearch book.
If there is a Logos account for the same email address, your Wordsearch books were added to it. If there wasn't a new Logos account was automatically created for that email address. If you had Logos and Wordsearch accounts with different emails, Logos customer service will merge the two accounts if you ask them to.
Some books from Wordsearch aren't available in Logos and there's a list
here showing the availability of every book in the Wordsearch catalog. A number of my books don't have a Logos counterpart, but I guess that's partly because I preferentially used Logos in the first place and usually bought books from Wordsearch that Logos didn't have.
At least for now, my Wordsearch software still syncs.