G series pieces

Part way through the Crown over W in circle marked range, the numbers were changed by the addition of a 'G' in front of the number.  The significance of this has yet to be established. Numbers start at G1689, but then there some seen that seem to restart the series at G0001.  More little mysteries to be sorted out, hopefully someone may have a catalogue that explains this.  For this reason, I have put the low number G series after the last high number ones.