NCperson -- I was able to confirm that the IRS knows that they have the $1,900 using the automated system. My instinct is to wait until closer to the deadline to see if our refund arrives, a new letter arrives, etc, with everything straightened out.
Between 20 and 30 years ago I was self employed and so paid estimated taxes. I always shot for over estimating, and so would get a hefty refund. I would use one year's refund as the next year's first estimated payment.
About 25 years ago we were on an extended out-of-town trip for 7 weeks in June and July. We came home to a huge pile of mail, including an IRS letter demanding money that had arrived a week after we left, which had been followed by another letter right before we got home that basically said "never mind" that had an equal/opposite adjustment. Because of how the mail was piled up I saw the second letter first.
So I do know that at least 25 years ago the IRS was sending out letters and then correcting things, all obviously automatically. And it was better to just let the computers do their thing without getting any human intervention to screw things up.
The letter has an 8 week response time, which is convenient if the computers can just figure it out in time.
