The answer I provided was specific to this individual's situation. In the case of the original question, only 64% of the individual's 2019 RMD had been satisfied (60% by QCD and 4% by non-QCD) prior to wanting to make a QCD of additional 4% of the total RMD. The individual appears to have interpreted the financial planner as indicating that no QCD can be made after an intervening non-QCD distribution, but there is no requirement that QCDs be made prior to other distributions. Certainly that QCD of 4% of the RMD would not offset the taxable amount of the 4%-of-RMD distribution already made that was not a QCD, but nowhere does the question ask if that would be the case. Upon making the QCD of 4% of the RMD, a total of 68% of the RMD would have been satisfied and 32% of the individual's RMD would have still remained to be satisfied for the year. Whether or not that 32% would be satisfied by making additional QCDs would determine the total amount that would be includible in AGI, but there could not be any less the 4% includible in income.
If the additional 4%-of-RMD was not distributed as a QCD, that portion of the RMD would still have to be satisfied by a non-QCD distribution, adding to AGI. By instead making that 4%-of-RMD a QCD, AGI is reduced from what it would otherwise end up being for the year. It's also possible that this individual had multiple IRAs and the original 60% of RMD satisfied the entire RMD for the account from which it was made, but because IRA RMDs are permitted to be aggregated and taken from any of the individual's IRAs, the additional 4%-of-total-RMD QCD made from this account would still reduce the AGI from what it would otherwise be since the amount of RMD that remained to be satisfied for the other IRAs would be reduced.
The fact that the non-QCD distribution was 4% of the total RMD and the additional QCD was also to be 4% of the total RMD might lead one to suppose that there was some desire to have one offset the other, but that would indeed just be a supposition. Nothing else in the question supports that supposition and other details in the question even suggest that this supposition would be incorrect.
