Exact situation here. My tellers also prefer to write down the amount on the MOs. I started doing so and more than one teller actually thank me for that.

I keep the receipts and stubs forever. Over the course of Years, I had to show the stubs once with my neighborhood BofA branch when over $5K deposit on Friday afternoon was reversed Monday morning. Their scan machine did not pick up the MO images and rejected the whole amount of deposit.

Yesterday one of the batches deposited, has a teller entry error - the last $ is a 9 but she put in a 3 - I did not catch it on the spot but saw it this morning the bank added $6 back as adjustment - the nightly reconciliation team must have caught the discrepancy. When that happens, the bad thing is the online images are gone - you could not see any image of the deposit slip nor the deposited items any more. That is where the stubs would become needed should later another adjustment occurred. (I always write the MO numbers on my deposit slips so each MO is readily identifiable.)

Several months ago the adjustment was to change a last 0.60 to even without cents - despite the deposit slip was correct - must be the very faded MO made the nightly reconciliation team thought it should be a 998.00 instead of 998.60. So the bank deducted 0.60 and all the images lost. I could trot down there to ask a review and got my $0.60 back, but of course I did not bother.