I have studied the Z-machine ("Zork"/Infocom text adventure engine), and I knew of some Infocom source files, but that is an impressive list! Strangely I do not see Trinity in your 2nd post (the list of games)... I mention this because Trinity is one of the few games published that *specifically* supported C128.
Well that is how I remember it I mean -- there was never a C64 or Plus/4 version of Trinity?
Anyway, for you creative artists reading this, you can create your own text adventure which is compatible with Infocom's Z-machine. Just use the program Inform... there are several versions available... the older versions work with more hardware (like C64) but have limited features, while later versions have advanced features that will only work on more advanced hardware (like C128).
So we know Trinity is missing... are there any other Infocom games missing? I am pretty sure there are more, but I don't know them off the top of my head...
More importantly, if you know where to find the source code for any of these "missing" games then please post!