Ulrika Ruding has a chapter in Wickman, Orrefors, that is the fullest explanation of the coding system used by Orrefors. The only problem is that many pieces don't seem to conform to that coding system. As Alistair Duncan says in his book on Orrefors, "There remain many marks that defy exact classification." Your rhino would seem to be one of those pieces. According to Duncan, the code for Alberius was "A" until 1980 (although Ruding says 1970, this can't be right, as Alberius started at Orrefors in 1971) and "OA" after 1980. So your piece was presumably pre-1980. He was known for his engraved designs and his sculptures with people and animals. I'd love to see a picture of the rhino if you ever get the chance.
Hope this isn't too much trivia. (Well, I know it is, but what good are obsessions without trivia?)