>> Perhaps a question for the osm forum?
I'm not *that* involved. Yet ;-D 

>> I could not found your tag wilt alt_... in the wiki.
Yeah, I did find a couple of mentions to use that tag for such a cases. But I haven't dug deeper. 
My concern is that if someone would search for 170 address specifically, they won't find anything. That's why I think this alt_ tag on the 172 node may be not sufficient. 