One stance does not a form make so you can't really decide on the origin of a form based on one of the main stances.
Which seems to be what you are doing.
From my understanding Hay Sa Fu Hung Ga added their IW from the WFH branch of Hung Ga, it wasn't original to it ( I could be wrong but I recall reading that and I think Gene mentioned that also).
The qigong in the TSK was present in Hung Ga before the development of the TSK, I think that Tit saw that it was good to put them all in one form ( by all I mean the bridges and "killing hands").
Whether there was modifications to it after that is speculative but I would think so, I mean why not?
I don't think the core, the "heart" was changes but having seen a FEW versions it seems that some of the footwork was modified in some lineages and the reasons were probably practical ones ( limited space for example).
Psalms 144:1
Praise be my Lord my Rock,
He trains my hands for war, my fingers for battle !