The standard testing regime that most type 2s stick to here, is to test at first bite of a meal and then two hours later. You’re looking at having a rise of no more than 2 mmol/l. So if your 7.4 is 2 hours after a meal but your pre meal reading was say 5.0 then the rise is too much and your meal needs to be altered.
In answer to your other question, if your HbA1c was 9.2% in 2014, you have done a good job dropping it to 5.8, however are you are you sure your 5.8 on your meter is an estimated HaA1c as a percentage, and not an average of your finger prick tests, I’m not familiar with your meter.
My HbA1c has been at non diabetic levels for over 3 years yet I am still diabetic. I continue to eat no more than 45g carbs per day to keep my blood sugars under control.