Not long ago I had an echo done after my ventricular tachycardia surgery. The initial report said my EF was between 20 and 25%. My doctor looked at it and told me that it's below 20%. Same test. I know my heart is worse now after the surgery because I feel like shit now. So it's under 20.
I've been living this since 2008, nearly 13 years now. It's not uncommon for me to have such results. I've talked with my cardiologists about this because I was concerned.
It's best to have the exact same doctor do your readings from the report. If your number goes up 5% but different doctors did the estimate, I'd not be too excited.