There were no computers back then. But they probably did run some war games with maps, counters, pencils and dice. They assumed the Germans would not attack through Belgium. Well, the Germans did. So whether the war games mean anything depends on the assumptions. If they handicap the Taiwanese forces to account for Murphy's Law, while adding resources to the Chinese forces in order to account for what they don't know about the Chinese order of battle, they've run an honest simulation. Otherwise, they're just deceiving themselves.
The American Plan Purple for fighting the Japanese in World War II called for the Pacific Fleet steaming from Pearl Harbor to engage the Imperial Navy in an epic battleship confrontation, with the Japanese Navy swept from the seas in about six months, while American garrisons in the Phillipines and Wake Island bravely held out.
In September 1939 there were five German divisions between Berlin and the west. Belgium and Holland could have mobilized thirty divisons between them. If the Belgians had invaded Germany in 1939, it would have been a race to Berlin, with the German army at the wrong starting line, engaged with a very determined Polish resistance. Of course, the Belgians and Dutch had concluded that it was not their fight.
No plan survives first contact with the enemy.
The PRC has to consider this as well, any invasion plan would depend on very fragile assumptions. The defense of Taiwan is probably more robust with respect to assumptions than its invasion.