Prior to the 1990s Taiwan had famility with the Colt 3x20 design, having both some production of the type domestically and having procured ArmaLite 2.75x20 marked scopes. Both these scopes were used with Taiwan's M14 rifles. Early XTS91 scopes show the scopes clear lineage from the Colt 3x20 design, externally appearing to be a Colt 3x20 scope with a larger objective lens, a new mount, and a castellated BDC knob.
Hopefully more to come...
Images
Early XTS91 scopes.
TS91B on Type 91 rifles of the ROC (Taiwan) military.
TS91B displayed at trade show and military demonstrations.