The Spreewerks are nice. The a/b-prefix guns were thought to be the last pistols produced with the a-prefix obviously preceding the b-prefix. There were however, Zero-series Spreewerks produced at the same time as the a/b-prefix guns. It is thought that the Zero-series (instead of a letter preceding the serial number, a '0' came first) were produced for a separate contract, possibly the Volkssturm, since the Zero- series pistols did not contain the typical E/88 proof marks, but instead used a simple 'u' and frequently an 'M' on the right side of the slide as inspection proofs. No evidence has surfaced however as to the exact reason the Zero-series guns were being produced.
Many Zero series and a-prefix guns made it out the door and were captured, but very few, if any, of the b-prefix guns left the factory. They were virtually unknown in the P38 world here in the US until the Ukrainian imports in the early 2000's. Some collectors believe that all b-prefix guns are/were Russian captures. No one can say for sure. Many were though imported and not stamped with the dreaded 'X' bythe Russians, nor were they import marked. A certain importer, now long deceased, made sure of that.
To answer your question though, a full run of 10k a-prefix guns were produced. The Zero-series guns made it to about 8k IIRC and I believe the b-prefix guns only got to around 5k. So the b-prefix and Zero-series were indeed the very last ones being made. There were a very small number (believed to be around 100) double '00' prefix guns made. But these were thought to have been possibly made after the factory was overrun by the Russians.
The grip-strap marking on your pistol is reminiscent of the markings on German pistols from the Imperial/Weimar era. My guess is it shows police use by someone in the post-war period.
Last but not least, Spreewerk was in Grottau, an occupied area of Czechoslovakia, not Berlin.
