the only thing I can state with confidence is that our operators does a make ready for every job at each process prior to starting production but the actual checks during production varies by the job quantity and operator experience hence the "regular interval". So they do the quality checks during production but its with varying frequency.
Would there be an encompassing phrase/statement that can satisfy this clause for this varying interval where it would not compromise what we are already doing in production?
The bit in red is potentially problematic for you, unless you can show that everyone does the minimum (defined!) testing, and others choose to exceed this.
As far as I can see, the only way to have an all-encompassing phrase for this will be to use one that doesn't really say anything, but instead points the reader/operator to a separate schedule where you've defined actual frequencies.
I still think you'll need to put that associated schedule together, as a live document so you can add new products/variations/production sizes etc, but so that you also still have a clear an unequivocal list so that (a) you have something against which you can train people, and (b) you have something nice and clear to show to your BRC auditor(s).