Having used a LJIII for many years, owning a IIp and had a IIIp at the office (we wore it out), I can assure you the cartridges for these three models were NOT interchangeable.
We have opportunity to obtain a number of HP 75A (HP 92275A) toner cartridges cheaply. The problem is: the HP 75A is compatible with a LaserJet IIIp. We have the discontinued model LaserJet III, and retailer specifications of the HP 75A cartridge omit mentioning our [obsolete] Laserjet III as an accepting printer. Can we actually use the HP75A on our old Laserjet III printers even though there are no acknowledgements of the fact, or is the HP75A really, truly unusable on our HPIII?s?