Adding on to the response you already received (re: Glogau), I would actually
suspect that this is a reference to the town of Gross Glogau, where the English
record keeper converted "Gross" to "Great" and then abbreviated to "Gt". I
believe this town is in Silesia (near Breslau, Germany; now Wroclaw, Poland).
I hope you can solve your mystery.
Searching: all in Breslau (and in)
FALK (Lissa) FREUND (Schmiegel) BACH (Inowroclaw-Tarnowitz-Myslowitz) PERL
(Kieferstadtel) IMMERWAHR (Brieg-Kreuzberg) SILBERSTEIN (Brieg)