Like any donated form, yours reflects the mental imprint of the author; e.g. there is no requirement or rationale for keeping track of aggregate cash totals. Some banks do track the number of CTR's filed, but I'm not sure how that would be connected to documenting exemptions. (BSA no longer talks about any retention period other than 5 years. There, the issue is when the clock starts to run.)
I know of no resource that explains this record retention requirement in detail, but I suggest you retain:
* DOEPs (or their equivalent) filed on paper as long as exemption is in place and be able to recreate a DOEP filed electronically for the same period of time.
* All documentation necessary to prove that an exemption was valid for five years going back from today.
My first suggestion is excessive, clearly more than the regulation would require. However, I've dealt with too many banks where examiners provided the list of exempt persons from the FinCEN data base and then asked the bank to produce the original filing for each of them. It's simply not worth arguing about.
In this world you must be oh so smart or oh so pleasant. Well, for years I was smart. I recommend pleasant.