This is pretty neat! One nerdy question, from someone who actually used to run Z-System (on a TRS-80 Model 4 and an Intertec Superbrain, for the record) -- why

This is pretty neat! One nerdy question, from someone who actually used to run Z-System (on a TRS-80 Model 4 and an Intertec Superbrain, for the record) -- why ZCPR version 1, instead of a later release? Is version 1 the only one with available source and/or a compatible license?