I don't know if this listing is just for makers who feature in the book, but there are many missing from the listing when looking through the Warszawa Telephone directory for 1938/39.
by A.J. Zawadzki
This is just one Warsaw maker not listed in the book appendices:
Elenberg Sz.. zakt, grawerski, Graniczna 3
There are also some typos to a few of the address lines in the dataset that I have spotted, one example in the appendix is:
Unger E., Chorążczyzny 7, Lwow
Whereas the 1928 Danzig and Poland directory it is:
Grawerzy, Unger E., Chorążczyzny 6, Lwow
small detail admittedly but IMO these should be correct in a reference work because the error has been perpetuated across other works and websites that reference the listing.