As many have already said, as the HbA1c measures a sort of 12 week average, a six week difference in test times will mean that you will have included 6 weeks worth of the previous HbA1c test, and who knows? A reduction to 7.4 is something to be pleased about, it's a move in the right direction. You've also lost 18 lbs, not to be sniffed at by any means so your hard work has definitely not been for nothing and has been rewarded, you just wanted a bigger reward.
I would just like to relate something that happened to me after 3 years of low carb. Those 3 years were brilliant, I'd thrown away the gliclazide, the januvia, even the atorvastatin (BTW, something your GP might consider in the short term to get to the 7.0 your surgeon is set on). However, my HbA1c tests started to come back over 50 mmol/ml (one was 59 mmol/ml). I struggled to work it out but realised that I was getting a lot of high readings in the morning, despite only having a low carb meal at 7pm the previous night.
In my case and it's not be for everyone, I cut back on the amount of meat I was eating and it did the trick, it's difficult to sustain for too long but for an important operation it's the difference between having the op and maybe not. I might seem a bit
Blasé but I've had to watch what I eat for decades and that's not an exaggeration. The discipline has done me some good.
You're doing all the right things, just needs continued perseverance and you will succeed. Negative thoughts become a self fulfilling prophesy, please try to stay positive.
As a reminder for myself as much as anybody:
Old unit = NGSP unit = %HbA1c
New unit = IFCC unit = mmol/mol
Old New
6.5 48
6.6 49
6.7 50
6.8 51
6.9 52
7.0 53
7.1 54
7.2 55
7.3 56
7.4 57
7.5 58
All the best