The version of ROM in your printer is printed on the startup page, vertically on the right margin.
You can also use the Apple Printer Utility to check what version of the IOP ROM the LaserWriter has installed:
1. Launch the Apple Printer Utility, select the zone in which the LaserWriter is located, click to select the printer, click Open Printer.
2. Click the arrow to the left of Printer Information, you will see the version of ROM and, depending on the type of LaserWriter, the version of PostScript ROMs also.