The oldest I’ve worked on is between the Mirtone 7900 and the Edwards 6500. I did an annual on an Edwards 6500 MK II in a condo building that was built in the 90s, with Edwards 439-6AWCs and 270-SPOs. The next day I did one on a Custom 6500 in a condo built in 1979, original to the building. The bells were Edwards Durabells, and the system had absolutely no smoke detectors, all heats & pull stations.
The oldest I’ve seen was a school in another city, that was being used as an adult education center. I have no idea what the panel was, but the horns were Simplex 4040s I believe, with simplex T-Bars. That system has since been replaced with a Mircom system, with mini horns.