Operating Pressure drop lower than 1mb at appliance, appliance badge shows 20mb

Hi
So i was at a job and took the working pressure at the meter, was between 19 and 23mbar
However at the gas fire (flavel emberglow classic) there was nearly a 2mbar drop
The appliance badge says 20mbar (which it was showing) but then its more than 1mbar less - is this allowed because manufacturers instructions take precedence or does it still have to be within the 1mbar drop ?

 

This is a pic of the badge