If you believe me then this could save you a lot of time for testing:
The $num() function has never been different.
Since very early posts $num() has been used to get the number part, mostly in TRACK, see e.g. here:
And the result for the conversion of a non-number results in 0.
Perhaps as a test you could use
%num(%artist%,2)
in the function Convert>tag-tag
as this has a preview.