When I obtained my licence OK3TRW in 1970 I lived in Bratislava, Slovakia. In the time of Czechoslovakia, prefix OK1 was used for Bohemia, OK2 for Moravia and OK3 for Slovakia. My licence changed from OK3TRW to OK1TRW in 1992 after I have moved from Bratislava to Prague. Short time afterwards, on January 1st 1993, Czechoslovakia split into Czech Republic and Slovak Republic. Czechia kept the OK and OL prefixes and Slovakia started using the OM prefix.