This article from the IRS website seems to explain what is going on. I also came here looking for answers, but after seeing the same thing repeated and not fully making sense to me, I thought to go to the source. So in my own case, I believe I am bullet #4 and have received a type of "plus-up" since it still says that my refund is pending.
"The fifth batch of payments began processing on Friday, April 9, with an official payment date of April 14, with some people receiving direct payments in their accounts earlier as provisional or pending deposits. Here is additional information on this batch of payments:
- In total, this batch includes nearly 2 million payments with a value of more than $3.4 billion.
- More than 320,000 payments, with a total value of $450 million, went to Veterans Affairs (VA) beneficiaries who receive Compensation and Pension (C&P) benefit payments but who don't normally file a tax return and didn't use the Non-Filers tool last year.
- Nearly 850,000 payments, with a total value of nearly $1.6 billion, went to eligible individuals for whom the IRS previously did not have information to issue an Economic Impact Payment but who recently filed a tax return.
- This batch also includes additional ongoing supplemental payments for people who earlier this year received payments based on their 2019 tax returns but are eligible for a new or larger payment based on their recently processed 2020 tax returns. This batch included more than 700,000 of these "plus-up" payments, with a total value of more than $1.2 billion.
- Another 72,000 payments went to Social Security beneficiaries who didn't file a 2020 or 2019 tax return and didn't use the Non-Filers tool last year.
- Overall, this fifth batch of payments contains nearly 1.2 million direct deposit payments (with a total value of just under $2 billion) and nearly 800,000 paper check payments (with a total value of over $1.4 billion). "
https://www.irs.gov/newsroom/irs-treasury-disburse-2-million-more-economic-impact-payments-under-the...
