It seems to me that you could accomplish that by setting [blInactive] to Yes
for everyone...
UPDATE tblDonors SET blInactive = Yes
...and then update the current donors like this:
UPDATE tblDonors SET blInactive = No
WHERE ID IN
(
SELECT ID FROM tblReceipts
WHERE Year([tblReceipts].[Date]) >= (Year(Now()) - 2)
)