According to a recent post Numista is only showing partial results because it is “slowly reindexing”.
I expect the process is reasonable and necessary, but while it happens people are getting bad results from research. Either they accept the results, accepting the bad information as true, or get frustrated because the see an error. But I can't see any notification of these bad known results.
When there is a known bad state for the search results there should be a notice on https://en.numista.com/catalogue/index.php both before and after searching.