Here's the evidence:
"Grätzer Bier is brewed in relatively small quantities by just two breweries in Berlin, namely the Monopolbrauerei and the Hochschulbrauerei."
"Die Herstellungobergäriger Biere und die Malzbierbrauerei Groterjan A.G. in Berlin", by Braumeister A. Dörfel, page 31 (my translation).
The original text:
"Grätzer Bier wird in Berlin nur in zwei Brauereien, nämlich der Monopolbrauerei und der Hochschulbrauerei in verhältnismässig kleinen Mengen hergetstellt."When it was first brewed in Berlin, I don't know. I wouldn't be surprised if it was after Grodzisk became part of the reformed Poland in 1919*. But I've no evidence to back that up. I could just be talking out of my arse.
What to call Grodziskie brewed in Berlin? I think we can all agree that Berlin is definitely in Germany and has been (or in Prussia) for a considerable length of time. Is it fair enough to call it Grätzer? Though obviously it wasn't brewed in the town the style is named after. It's got me scratching my head.
What do you reckon?
* That was a shit guess. The Josty brewery was already brewing a beer called Grätzer in Berlin in 1900. (Thanks Robbie.)