[Talk-GB] Correcting an error when the only correct data sources are non-open

[Mark Goodge]

I've just updated a couple of retail units in my town that have recently 
changed hands and now have new tenants, to replace the old names with 
the new ones and update the ancillary tags appropriately. So far, so 
good. No problems there.

However, in the course of doing so, I decided to have a quick click 
round some of the other nearby units, just in case I could fill in any 
useful tags, and found that one of them had the wrong address - 
specifically, the wrong number (it should be 16, but was given as 14).

Now, I know what the actual address of that location is, from previous 
knowledge of that particular unit when it was in the hands of a friend 
of mine, and both the local council's property database and the Royal 
Mail PAF agree with me, as does OS Mastermap. So I am certain that my 
knowledge is correct. But... I can't find any open data source which 
says the same thing. And, annoyingly, the current occupant's own website 
has the wrong number on it (which is where I suspect that the previous 
mapper got their data from).

I've made the change anyway, and tagged the source as local knowledge 
(which, in a sense, it is). But my change is vulnerable to being 
reverted by someone else who goes by the occupant's website, and I can't 
use the PAF or Mastermap as sources in OSM as that's not open data.

What would other people do in this situation? How do you correct an 
error when the only correct sources are non-open?

Mark