Some Tlds will not work. Scrapebox uses WHOIS data to determine if a domain is registered or not.
First it does a GET request and if the page loads, obviously its not available. If it doesn't resolve then scrapebox does a WHOIS Check.
Some registrars return the same data for every single domain whether or not its registered. This problem is made worse by GDPR. For example, I tried to build in .club. However .club returns the same data and just says its all redacted, even for unregistered domains it shows them as having a creation and change date of when .club its self was created as a registry.
So unless the GET response succeeds scrapebox is unable to accurately determine if the domain is available or not.
In fact GDPR will probably cause WHOIS to pretty much be useless and go away over time. It was already something they were working on for years to standardize it and make data private, but GDPR pretty much put the nail in that coffin. So in years to come I expect that WHOIS usefulness as well as functions and tools built around it, all tools, not just scrapebox, will be diminished in effectiveness if not depreciated entirely.
I don't work for Scrapebox, and thats just my opinion. However specifically to your questions, for some smaller tlds scrapebox won't be able to provide you with the accurate info for all domains.