To me, that Bass looks to be a Wilfer (Juzek brand labeled import) and not a Pfretzschner. In my readings I have learned that all the members of the Pfretzschner family were Bow makers and not Violin makers with one exception and that was C.F. Pfretzschner I, II and III from the late 18th century on into the early 20th century. G.A. Pfretzschner is actually listed as a Bow maker only! I believe that his name was used for labels in instruments imported from Germany after 1900. Morelli and Juzek are two other 'import' names used as well in a similar manner.
Age wise as a Wilfer I would put that Bass after WWII and not WWI. The Purfling design under the Back Button does not look like the Pre-war Bass I have seen by Anton Wilfer bur rather the later ones I believe by Wenzel Wilfer a.k.a W.B.W.
How that Bass has a Pfretzschner label can be any number of reasons. Here is a picture of a typical Pfretzschner label from a
Bass I once owned;
The design in the Back as seen here used by
Pfretzschner is quite different that your Bass.
The Label pic you posted is not very clear. Please tell us exactly what it says. Mine says;
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Artist Deluxe Model (hand written script)
Andreas Morelli (printed in script)
Handmade Reproduction (printed in script)
Antonio Stradivarius (hand written script)
Trade Mark Registered
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I have seen Basses exactly like mine in both 3/4, 7/8 and large 7/8 (4/4) that had either a Morelli label like mine or a G.A. Pfretzschner label inside the Bass.