Unfortunately when it comes to HUMs limits the intial values set by the manufacturer can be miles out and only through operational experience will accurate limit values be found.
That doesnt mean testing to destruction but a gradual increase in limits from very low intial values. The idea is that the limits are accurate components coming back to the shop for failing vibe levels are actually buggered not 90% expensive false alarms.
Only then can you have faith in HUMs.
B412 BHVMS is a good example, Bell had lots of knowledge of vibration levels from the Canadian Griffon HUMs system but as it was military technology they werent allowed to use it for setting civilian values.
SO we all went through a few years, still going a little bit, of pulling stuff off that was pefectly fine.
HUMs is only one tool and its not to be followed with blind faith.
Its all about the interpretation.
All very well for a new aircraft type (if it had be a 225 M'arms) but the L2 has been around a long time so all thresholds should be set accurately.
Again it appears the MGB was in alert so that to me tells me that the thresholds were set correctly