What's the best way to identify data gaps when treatment == PREVIOUS

We have PointPhysicalMeasurement data for which the treatment is PREVIOUS. As a result, the system returns the latest value prior to the requested time and there appears to be no gaps in data.

I was thinking of using a tsDecl to attempt to override the treatment to AVG or even COUNT since it takes treatment as an input, but curious if this is viable or if there’s a better alternative to identify gaps in data over a specified time period.