Those values are in fact text
If I was to just add the "" around them within
your formula it will still work, correct?

Yes:

=SUMPRODUCT(--(Main!$F$2:$F$5000=A14),--(Main!$F$2:$F$5000<=B14),--(ISNUMBER(MATCH(Main!$X$2:$X$5000,{"2021","2022"," 2023","2025"},0))),Main!$K$2:$K$5000)

Can't the 3rd term inside your SUMPRODUCT, which is this...

--(ISNUMBER(MATCH([Main.xls]Sheet1!$X$2:$X$5000,{"2021","2022","2023","2025"}, 0)))

be simplified to this...

--([Main.xls]Sheet1!$X$2:$X$5000={"2021","2022","2023","2025"})

(since it would occur inside a SUMPRODUCT function)?

Also, on an "off topic" note...
Did you receive the private email I sent you on Sept 2nd?

Rick