OK, I added the two series, for the B&H and NMA numberings.
The origin of the third numbering, which differs from both of the above for some sonatas (K 301–306, 379, 454, 481, 526, 547), is favoured by the IMSLP pages (though not in the actual titles), Wikipedia, allmusic (not thoroughly checked but at least for some), is still a mystery to me. And I found one set of Hyperion releases that seems to use it on the front covers:
- https://www.hyperion-records.co.uk/dc.asp?dc=D_CDA68091
- https://www.hyperion-records.co.uk/dc.asp?dc=D_CDA68092
- https://www.hyperion-records.co.uk/dc.asp?dc=D_CDA68143
- https://www.hyperion-records.co.uk/dc.asp?dc=D_CDA68164
- https://www.hyperion-records.co.uk/dc.asp?dc=D_CDA68175
I wonder if this should be added as a third series. I’m hesitant to do so without a definitive source but it does seem to be moderately widely used.