Thanks for your input.
Yes, I did replace the URLs with this tool: https://interconnectit.com/products/search-and-replace-for-wordpress-databases/, yet for some reason the records of three pages still got corrupted.
At first, permanently deleting the three pages did not “free up” the original URLs. For some reason, however, letting it sit over night did the trick and the following day I was able to reuse those original URLs without a problem.