Pro Patria medal with year clasp/bar.

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I recently bought a Pro Patria medal with a 1988 year clasp (photo by Gribbo). I have never seen a Pro Patria that was issued with a year clasp, if it is a year clasp at all. Was 1988 the year of issue in which the recipient has completed his 3 months+ border duty? If so, why are there no other Pro Patria medals with these year clasps to be seen? Can somebody with medal knowledge shine more light on the question? I only know about the Cunene clasp issued with the Pro Patria medals of the mid 1970's for participation in Operation Savannah. Thank you.