Just checked the rules and by logic it seems the answer to the question is: yes.
I interpret the rules so that a TRS containing cargo that was loaded a previous turn can move during the CM as part of an invasion force but does not HAVE to unload its cargo (wouldnt even be allowed if the cargo was a AAA). If loaded in a previous turn, the TRS can unload any or all its cargo during the invasion, and any remaining cargo during the NCM or not at all.
Reading the rules I Imagine a slightly different example:
You canNOT load flak into a TRS during the CM, because those units can by the rules not unload during CM, they may only move during NCM, “except when moving with a TRS if loaded in a previous turn”.
So, the flak, if loaded in a previous turn, may move with its TRS and another INF loaded during the CM this turn, may stay on the TRS while the INF must unload. Then, if the territory is taken, the flak may also unload during the NCM.
If the flak were an ART, the same above story goes for this ART instead of the flak, except that the ART has a choice. It may unload during CM or it may unload during NCM. Thus, if both the inf and art were loaded in a previous turn they would both have that choice.