Sorry if I was not so clear
I'm writing about field EQUI-EQUNR (equipment number) because that's how I understood the question. You can use internal number range for this or external one (manual assignment of equipment number during creation). Of course I'm aware about usage of TECH ID, and totally agree with your idea (usage of internal number range for EQUNR) and assignment of different equipment ID to TECH ID field). In fact that's what I'm doing during migration of database from external systems to SAP.