Turks

I agree with Bronco, wait for your decision letter and it will explain what the VA did. I recently won an EED (Earlier Effective Date) several years ago and the VA paid me two separate retro payments. One for my initial payment and one for the fact that my rating had went above 30% for my dependents. So, try to take a deep breath and wait for your decision letter.

You wont know for sure until you get the envelope.  What do "letters" in ebenefits say?  That, also, may help.  
Also likely:  
    You figured your back pay based on the effective date on ebenefits.  Ebenefits effective date is almost always wrong.  They put the date of "the last Cola" which would be Dec. 1, 2020.  And. that is rarely correct.  You wont know the effective date until you get the envelope.  

Turks . Welcome to Hadit. Don't know. You asked "is it possible that the VA has messed up?" Yup; we're talking about the VA here. I would just call Peggy, 800-827-100, and tell the rep what's going on. You can ask for an audit, but really, you need to get your decision letter to understand what their position is currently.  But you are on the right path though. If they overpay, they will eventually come after you. If you're pretty certain, set aside the extra so it doesn't hurt so bad when they come after you.