In message , thoss
writes

Those apostrophes are fine. But I also have, dating from an earlier
age, Philips' Modern School Atlas, published by George Philip & Son Ltd.
I wonder what that one is doing there.

George Philip & Son used the forms Philip's and Philips' totally
interchangeably for a very long time. I even have a copy of their 1862
London map which is entitled "Philip's New Plan of London" on the map
itself, but "Philips' Guide to London" on its cover.

There never has been much consistency in the use of the possessive
apostrophe in the case of words ending in s.
--
Paul Terry