There are other OLCI restrictions. If your itinerary ends in TPE you might get flagged for document check/proof of onward travel. So, no OLCI for you. BR, CI and CX are the three airlines that truly care about this (perhaps they were fined too many times for bringing inadmissible pax to Taiwan). If your itinerary starts in TPE, they might want to make sure you will be let out at the border (otherwise, your luggage would have to be unloaded later, and perhaps your seat can be given to somebody else if the flight is overbooked). For foreign visitors, this generally involves manually checking your passport for entry dates to make sure you didn't overstay. If your redemptions are one-way, one of these might be the reason why OLCI is not available.