There are three separate DXCC entities involving OK, OL & OM callsigns, as follows:
|ADIF Name||ADIF DXCC No||DXCC status|
The above information is taken from the ADIF specification, http://www.adif.org/adif227.htm#Country%20Codes
How is all this related to dates and prefixes?
|DXCC||Valid QSO Dates||Prefixes|
|Czechoslovakia||Before 1993-01-01||OK OL OM|
|Czech Republic||1993-01-01 to now||OK OL (ex OK1, OK2)|
|Slovak Republic||1993-01-01 to now||OM (ex OK3)|
The above information is from the RSGB Prefix Guide.
Why do I get error messages about OK, OL & OM in my upload report?
You get these messages in cases where your logging software does not map these callsigns according to the above information.
In these cases, you should encourage the person who maintains your logging software's country database to update the mappings in accordance with the above.