I am making the corrections to my final project which we discussed in the lab. I remember now why I had put the Troparion after the Great Doxology as of the Nativity: In the HTM book it indicated that the service is chanted as on the 25th with the following changes…..It had a list of changes and the Apolytikion following the Great Doxology was not one of the changes indicated.
Although I just checked Demetri Khoury, and he indicates that it is “Today is Salvation.” So I think I had missed that, and just assumed something that was incorrect.