What is the correct way to use KeyNeedsToReplicate()

I am looking at 4.16 code, and it seems DataChannel used SubobjectNakMap as key info recorder, which have limited size as 64. I think this may result info lost when nak is detected with 64 packet skipped.

So my questions are: If I use KeyNeedsToReplicate(), how to ensure data is correctly replicated to client? is this mechanism working now in UE4, or it is abandoned?