I have copied the information I need before the moderator removes the serial numbers. I must say you have a setup I am not familiar with at all not to say you don't have a valid post for the open forums for others who use your methods. I have not been able to find the previous User Guide for this unit today but I may be able to obtain it. I want it so I can find if the correctly working printers have been restored to default or if the printers with the larger font on the test page need to be restored to factory defaults.
Have you done any additional troubleshooting to the two printers in particular? It does seem the two you are having problems with were possibly first generation printers. I am going to do some additional research that will likely take me longer than a day to look into. Any additional information you have to give will be helpful while I continue researching this such as the use of a different USB cord, maintenance done, etc. Thank you for your patience and I am happy these 13 year old printers are still working for you.