Hi Mario
i suggest using this regex
[a-zA-Z]{3}[0-9]{2}-[a-zA-Z]{3}[0-9]{2}
this will find jan14-DEZ14 as well. Or both written in lower case. If you are sure, that you only use upper case charactes you can go with this one:
[A-Z]{3}[0-9]{2}-[A-Z]{3}[0-9]{2}