It was pointed out to me that this marking not only occurs on the XO dated boxes. but on the XR dated box that I have (I am away from my collection as i write this). Bob R also points out that his XH box does not have this marking. If I understand Bobs posting, it looks like the side marking on the XH box are slightly different with the powder designation in larger letters and the top line not in bold print.This likely indicates a second printing of these boxes.
This is important because it may help us sort out the month codes for Geco. We think we know all or most of the letters used for the months, but not the months they apply to. Four of the letters spell GECO and we suspect these are the first four months (Jan-Apr). if this assumption is correct then the XO boxes are from April 43.
If we assume that the four documented months of production are sequential, than the XR, XU and XH codes would represent one of the months of May through July. The XR box has the same 0/0464 marking as Bob’s XO boxes so it may be from May 43. John M gave a detail description of his box and didn’t mention the 0/0464 marking on the tab so that means his XU box and the XH boxes would be from June and July. This information could get us about half way through the Geco month codes.
If anyone has anything further on these boxes and cartridges, please add to this thread.