As a person who works in the science/medical field, you'll find more often then not, grey answers, instead of black and white. Everyone expects docs to give them absolute, black/white answers, but it is not always that easy. Your doc was being honest.
You also have to remember most all of the meds prescribed for MTF HRT are being prescribed for off-label purposes. Estradiol (Estrace) pills as produced by Warner/Chillcott were designed to be used by cis-females for birth control... Not by trans-females on HRT. Same with Spironolactone. It's was designed to be a high blood pressure med... And odd side effect was determined that it could block T production and receptor binding. As a matter of fact, Spiro is rarely prescribed for high blood pressure anymore, because there are many more effective and newer drugs on the market. So what these sort of drugs, used not for their original/designed purposes over an extended period of time which they also weren't intended for, is to put it colloquially... A crap shoot. There have been some long term studies to try to determine the long term effects of HRT IN MTFs... But not enough to be conclusive.
Also few docs have experience prescribing trans HRT... So unless they had a previous trans patient, they would have zero idea regarding dosages, blood work, et al. Find another doc, endocrinologist, gynecologist, that has previously trans patient experience. You don't want to be any medical professionals first trial patient.