I have also noted that L-W's KTB's are quite "telegraphic" in places and it's hard to get many specifics about the real-life encounter but K-L Hirsacker's KTB from U-572 makes it very clear that U-572 was the boot that U-96 encountered during their chance meeting ("we have only 12 U-boots in the whole North Atlantic and here we are almost colliding with another one in a storm"). It appears that the boats exchanged signals by blinker lamp and Hirsacker recorded that he confirmed that the boat that he met was U-96.

And I wonder if Hirsacker's later accusation and trial for "treasonous activities" is reflected in "Thomsen's" "Here's to our omnipotent and all-seeing Fuhrer, who rose from being a corporal to the Greatest Military Strategist Of All Time" speech in the bar/nightclub/cathouse before U-96's sortie in "Das Boot". Maybe Buchheim was aiming closer to the mark of a real person than I'd thought.