What is more it is not the PZL P.23B but PZL 23B The letter "P" was used for Pulawski's fighters only. Both pics above show planes of the 41 Squadron and both bombers were crashed in 1939.
Ah yes.. this is a book from 70' and the kind of marking was used at that time. To be honest in the pre-war and post-war time there was quite a wide margin of discretion in writing of the markings. You may find both versions of that used for both fighters and bombers. However there is the pre-war advertising material of the PZL factory for PZL P.24 and PZL 23 (see the link below) just with the kind of markings for the planes. And now these are considered to be the correct ones and used in most of publications..