Curious about test results

Hello everyone! I am 76 male and my Doctor says my kidneys are good with my gfr being >60 I get blood work done every 3 months because I take methotrexate for “suspected RA”! Doing great with that. Anyway my Creatanine is 1.14, which is typical for me over the years and her estimated gfr for me is always above 60. I just noticed another result on a graph showing my egfr going from 60 down to 44 over the last few years but she says my test results are normal but I don’t understand this discrepancy
Obviously she knows something I don’t lol. In great health I anm lucky to say🙂 Any ideas?