Your Libre is taking all of your data and working out what the average levels have been, so in reality a true average.
I know everyone calls the HbA1c an average of your blood sugar over the last 12 weeks, but of course it is not really an average at all.
The HbA1c is measuring glycated haemoglobin, the higher your blood sugar has been over the lifetime of your blood cells, the higher your HbA1c will be. Blood cells usually live for around 12 weeks which is why they call it a 12 week average.
But how long do your blood cells actually last, 11 weeks, 10, or maybe 13? Who knows. I could have the same HbA1c as you but if my cells kick the bucket at 10 weeks and yours hang around for 13, my blood sugar will have been much higher than yours for us to have the same HbA1c.
So HbA1c is a useful tool to for Dr's to diagnose and assess our progress.
Your Libre is giving a true mathematical average worked out from your glucose levels.
If the two numbers were to match, it would just mean that your blood cells are behaving themselves and turning up their toes on their 12 week birthday.