My HbA1c looked fine but my CGM told a different story

I've recently started looking beyond HbA1c and I'm trying to understand what all the CGM numbers actually mean.

I keep seeing terms like time in range, GMI and glucose variability, but I'm not sure how they add extra information compared with a regular HbA1c test.

Can someone explain what these numbers tell you that HbA1c might miss? Are there situations where someone can have a decent HbA1c but still have problems showing up on their CGM?