Is it not the case that StY is reputed to have some expertise in scanning? Note that the spell might be easily performed by Paarfi but actually sorting out the results might involve calling a lot of library methods from the Orb and pulling up databanks of typical and atypical genomes. This might be a drawn-out process involving tweaking of parameters. And according to my Yendi cuckoo theory it might be non-trivial to distinguish a Dragonish Yendi changeling from the real thing compared to doing a simple House-A-or-B separation. Incidentally, I wonder if there are any sex-linked House traits.