My most recent day 2 fsh value was 12.7. ecl assay gives a range of (3.5-12.4). let's say another woman got an fsh value of 10 at a lab that used an assay w/ range of (1.9-8.78). this woman would consider her fsh far lower, but in reality, is it?

Most hormone tests are standardized so that there is typically one range for all of them. The one variable is where in your cycle are you. FSH levels tend to range from 1.4-9.9 mIU/mL during the first half of the menstrual cycle before rising up to 17.2 mIU/mL during ovulation. Talk to your Dr about what an abnormal lab result means in your specific case.

This will depend on the day to day variation in the assay it self in the lab. And if it was done on same day. Best to repeat it.