I find some aspects of this very odd, the standard ZEN connection is
"Zen Internet provides our Fibre Optic Broadband (FTTC) services on the “Speed” option. A connection should drop no more than 20 times in a 24 hour period, and should error no more than 2 times per minute."
This would mean that a resync would in effect only be noticed via the error count. Unless you have 20+ a day of course! However a line error caused resync event is what most would regard as the one event that the DLM really needs to avoid happening.
If they are intended to spot resyncs caused by errors, then I am not sure of the errors. 120 ses or es an hour can easily conceal a resync event whilst 2 per min is common. 120 CRC/hour (2/min) is possible but it does seem too strict. On the other hand I think it really is a big CRC event that is more associated with a resync than a big es and ses.
I have to say I feel as though were only being given a general idea and not the much needed detail that you need to make some value judgments.