Comparing data in multiple rows

bimalaar, I might be missing something but presumably you can make the assumption that Feedback is always sent post Donation ?

If so see the attached, sheet DOTE ...

In short I sorted the data by Donor and Feedback date .. this makes the analysis much much simpler based on the above logic re: feedback/donation dates.

Given the volume of data in play I feel this method will be far more efficient than leaving the data in it's present order and calculating using a complex LOOKUP approach...
As it is a one-off exercise post-completion you should copy and paste the results column as values over the formulae and then resort as desired (the final column is in place to facilitate this process... or dispensing with this column just sort again by Donor/Donation Date)