Charitable Deductions

That's not how it works.  Taking the standard deduction doesn't free up the 'unused' charitable to carryover.

Oh - I forgot that $ 300/600? you got if you weren't itemizing.  There's a box to check somewhere on the itemized deductions 'page'.  But I'm a Lacertian - ya' need a PS person to stop by with the specifics

That went away after 2021. it was a  temporary provision of the COVID-19 relief legislation.

Were they cash contributions?

I think you need to enter it on the worksheet on Schedule A where you list the charity name and amount, not directly on the Schedule A line.

I think that for at least one of the years you had to enter it directly on the 1040 Worksheet (maybe both Schedule A and the 1040 worksheet; I think there was a mini-worksheet on the 1040 Worksheet).

Sorry, missed the 2020, as a side note you only have until 5/17/24 to get a refund from 2020. You enter charitable donations ($300/$150 MFS) directly on 1040/1040SR worksheet line 10b. note for 2020 everyone could only take $300 per return except MFS was only $150.

Just wondering are you going to charge them for the extra work/research and figuring this out? If they are in a 15% bracket and it is a $300 amount, than they saved a whopping $45 in tax.