Hi.
Sorry for my late reply.
Well, first I thought that it looked really amateurish, so I checked with overpass if this is somewhat common. Turns out it is not. There are only around two other buildings in England with 'staircase' in its name. 

Then I saw that it was mapped by an intern (mprhode) around 9 years ago. So I thought that he/she either didn't know about the addr:unit tag or it wasn't established yet. 

Personally I  think that the map looks cleaner this way and there is no reason to spell it (staircase) out when there's a tag for it. It's also a misuse of the name tag.

But it's up to you. If you think my changes are better undone, feel free to do revert them. No hurt feelings! :)
I started adding the add:unit tag to a few other colleges in Oxford but stopped after you contacted me. 

If the staircase number is not part of an actual address, as you said, it could also be mapped using the ref tag. Wdyt?

Cheers, 
Lukas

