When you run mkdev parallel or the Hardware/Kernel Manager and select Modify configuration of PCI parallel ports to add or remove PCI parallel cards, it is important to note that you are specifying the total number of PCI parallel ports that you want configured for your system -- not the number of parallel cards on your system. For example, if your system contains two PCI parallel cards, one with two ports and one with four ports, you would configure your system to support six PCI parallel ports.
PCI ports are enumerated at boot-time. The first port that is detected is designated /dev/lp3, the second is /dev/lp4, and so forth if you configured the system for more than two PCI parallel ports.
For instance, if your system contains a single-port PCI parallel card that is configured as /dev/lp3, when you install a second PCI parallel adapter, it is possible that the new card could be designated /dev/lp3 and the original card moves to /dev/lp4.
If a printer is attached to a port that is modified because of changes to the total number of ports on the system, you will need to modify the configuration for the printer.