I bought a Christian Reisser Double Bass at auction

I spotted this huge violin for sale at a local antique auction. I went along and saw that it was lot 264 so I had to sit through a lot of items for 2 hours before finally getting to the giant violent. I stuck my hand up, I was bidding against a commission bid in the auctioneer’s book and am happy to say that I finally won, and stuck it in my van

ChatGPT says “That label is from Christian Reisser, a violin and double bass maker (Geigenbauer) based in Ulm, Germany, active roughly early- to mid-20th century. The phrase “ULM/DO: HINTERM MÜNSTER” means “Ulm/Donau: behind the cathedral,” describing his workshop’s location. “FERNRUF NR. 2198” is an old-style telephone number, placing it pre-1950s. Reisser of Ulm appears in Geigenbauers Lexikon (Jalovec, 1958) and in several German violin maker registries listing him as active around 1920–1950. If original and intact, a Christian Reisser double bass could have collector or player value, typically £2,000–£6,000 depending on condition and tone quality.

I asked ChatGPT how it knew this info and it said:

“From offline reference works and archival trade listings I was trained on — mainly Karel Jalovec’s “Enzyklopädie des Geigenbaues” (1958) and Lütgendorff’s “Die Geigen- und Lautenmacher” (1922–1954 editions).
Those include a Christian Reisser, Ulm/Donau, listed as a violin and bass maker active mid-20th century, address Hinterm Münster, confirming your label’s text.”

Seems like a good one then? It’s weird because if you google Chrisian Reisser, you get no results. Hmm. Anyone know what’s going on with this bass?

Update: I got told to ask a particular chap online who knows about double basses and he responded as follows

p.s. is it Reiffer or Reisser? Hmmm