In the meantime I have received a response from Glasi management, and have done a bit of additional research myself.
Willy Steinlin (the designer of the OLMA series) ran a design studio in St.Gallen from 1971 to 2003. There are actually two slightly different versions. What you see on the
Glasi web site today is the version of 1992, the result of a collaboration between Willy Steinlin and Glasi, and produced exclusively by Glasi.
The moulds of an earlier version were likely kept by Willy Steinlin himself, and he had the items produced by both, Glasi Hergiswil, and Sarner Kristall-Glashütte (closed many years ago). These moulds seem to have been lost when Willy Steinlin Design closed in 2003.
Conclusion: Pete's item will most likely be the earlier version of Willy Steinlin's design - and could have been made in either Hergiswil or Sarnen.