Good morning,
these piecemeal bits are not sufficent to prove that the 128 are or are not a hoax.
The best assessment of this topic that I ever read is the article that
falkeeins linked in post2.
I've also worked through this Dahl biography:
https://www.amazon.de/RITTERKREUZTR%...s=walther+dahl
but despite being enjoyable to read it rather uncritically features a 128-kill-list.
I hope one day we will find a contemporary statement or a rudder photo or another primary document that clarifies the matter totally.
Cheers,
Michael