I think the reference should have been to NEL at Glasgow who are now a commercial operation. They operate flow calibration rigs of various types but not really on an "industrial" basis i.e. they are academics & don't have the same pressures as we mere "working engineers"!!. I think you will also...
I think you seem to be on the wrong lines. AS one subscriber already advised the Cal system is really an aid to ensure you maintain & support your QUALITY standards, that means YOU decide what standards an instrument must meet & the system tells you WHEN any device is due for routine calibration...
Frequency of meter proving will generally be set by the Regulating Authority concerned if a Fiscal type system. Otherwise the frequency will depend upon the actual process conditions,fluid quality (clean/ dirty etc.) & obviously the level of uncertainty you need to obtain.
As a general...