I am not sure that you are right on that point. A lot of items has not been signatured, as I understand it, it was only done when the time was to it, and therefore a lot of Holmegaard production has no signature.
The signature you refer to, is mostly found on drinking glass and offcouse the HG stands for Holmegaard but the number most likely refer to the number off glass i a series, beer HG1, redwine HG2, whitewin, HG3 and so on, but only in that glass series. If you have Shipsglass redwine with HG2 it do not means that Tivoli redwine also have HG2 it can be a differet cifer.
If we are talking signature on vases, bowls ect. they may be with signature HOLMEGAARD 15768, where number is stock item number, this number can later on be another number, due to chance in stock program, although it is the same item it could be with a signature like HOLMEGAARD 2001234.
The there is all the designer signature often like HOLMEGAARD 19PL76 or HOLMEGAARD MB80 and so on, the most found signature is:
PL - Per L√ľtken
MB - Michael Bang
JB - Jacob E. Bang
C - Christer Holmgren
SW - Sidse Werner
Hope this clear up a bit on Holmegaard signature.