Actually sort of in reference to the BSG-75 argument.
The BSG may be referring to Battlestar Group 75, while the Galactica number may to something different. Assuming the creators and researchers are basing this off of US Navy naming convention (they very well may not be), but a carrier oftentimes is referred to by 2 different systems. One is CVN-XX, that being the ships actual designtion, and the other is CTF-XX, which is the carriers number COMBINED with the air groups designation.
Sine the Galactica is mentioned as being the last of the first twelve Battlestars, is actual designation should be BS-1 thorugh BS-12, take your pick. Its embarked air group would have been some designation whose number added up to 75, so BSAG(BattleStar Air Group)-74 through BSAG-63. Both of those in composite would have been BSG-75.
Thats my working theory at any way. Since it was one of the original 12, I fail to how its designation could be 75 without somthing like the above happening