OK, thanks, but the biological/curation issue behind the numbers above is as follows:
It looks like Swiss-Prot have included a large number of proteins (in the order of ~ 500-800) that HGNC are not classifying as protein-coding. The largest categories I think (by manual inspection of matches from segments from the Venn I put on twitter) are endogenous retrovirus, long non-coding RNAs and odour receptor pseudogenes. This is numerically dominant over the relatively small one-to-many (SP < > HGNC in both directions as Jerv shows) which I think they agree on as proteins.
After some hours of head scratching, cross checking and making Venn intersects (see twitter) I think I have an explanation. So no one needs to dive into this if they have better things to do, but I will hold off on my conclusions for a time just to see if anyone wants to come up with an independently corroborative explanation (which I actually think is important for the domain of protein annotation)
Thanks for all the comments, I managed the review in the end "Last rolls of the yoyo: Assessing the human canonical protein count [version 1; referees: awaiting peer review]" https://f1000research.com/articles/6-448/v1 feedback welcome