Since you are cataloging Tiffany, including a lot of historical data, why not include the dates and studios that did the restoration work? This info will and should become part of the historical provenance.
I am recording and displaying this when known (so I will add this information for this window in next time I update the website) but I only have restoration information for about 130 windows so far. It's one of the attributes where nothing is shown if there is no data, rather than a blank entry. I could easily change that but I didn't want too many blank entries so there are a few attributes like that.