If it was always called Olzstyn in Polish, I stand corrected. I was perhaps confusing it with Ketrzyn, formerly Ranstenburg. (Is this a transliteration into Polish of Allenstein, as Frombork is a transliteration of Frauenburg?)

However, before 1945  the town was known to non-Poles as Allenstein, as a glance at any contemporary travel guide will attest. Witness also the League of Nations plebiscite in southern East Prussia, which as shorthand was referred to as "the Allenstein district" (Cf. Churchill's memoirs). The plebiscite there in 1920 produced 97.8 percent (362,209 votes) for Germany and 2.2 percent (7,980 votes) for Poland.10  These are facts, widely reported at the time and cited in countless historical accounts since then.

By the way, it would be interesting to know what happened to the Masurians who used to live there.
 User:sca