I've sent the contents of your invoice.pcl.txt file to my two local printers; in each case, a single page is printed, as follows:
On both printers:
- A logo is printed at top left;
- Various pieces of text are printed in various different fonts; some of these text fields are enclosed within printed boxes.
On the LaserJet 1320n:
- A Code 39 bar-code is printed towards the top-right;
- The same bar-code is printed bottom-centre of the page;
- A Postnet bar-code is printed about a third of the way down the page, on the left;
- A different Postnet bar-code is printed near the bottom of the page, on the left.
On the LaserJet Pro 400 Colour MFP M475dn (a more modern device):
- Plain text is printed instead of each of the Code 39 bar-codes;
- Plain text is printed instead of each of the Postnet bar-codes.
So the more modern device (of a similar vintage to your LaserJet M401) doesn't print any bar-codes at all.
Note that neither of these printers has any bar-code DIMM or cartridge fitted.