Dear TKS ji,
You had mentioned earlier in another post that Gayatri Chandah is employed for Homas.
But Nicruth Gayatri Chandah is employed in Ganapathi Homa where Ganapathi Athrava Seersham is recited and it has Nirchruth Gayatri for its Ganapathi Gayatri as evidenced by :
Ganaka Rishi:,Nichruth Gaayathree Chandha:, Ganapathir Dhevathaa, Om Gam Ganapathaye Namah.
Eka Dhanthaaya Vidhmahe Vakra Thundaaya Dheemahi Thanno Dhanthi Prachodhayaath.
So its kind of still unsettled as why there are some exceptions to the rules..I am pretty sure we are missing out something here.
I do hope to find answers soon...I know all these are Pre Paninian..so not looking for a Paninian answer.
What I said was ONLY with respect to use of Gayatri Mantra and which meter is used when.
If there are 23 syllables in verses chanted in other Homa they can employ Nichruth Gayatri Chanda meter. There are no issues.