I've read a reasonable number of research papers investigating various aspect of #T1D and a lot of scientists rely on HbA1c to judge the impact of what ever they are researching...
IMO this seems to entirely miss the point 9/10 times.
#Diabetics actively manage their BG so something can be having an effect, it can be taking more effort to control BG but Hb1Ac remains unchanged.
Hb1Ac isn't a good measure of impact.