I haven't seen any ads or packaging mentioning new models or improved brightness or anything, like they did with the primary cell lights. Be interesting to know. I do know halogen bulb technology didn't go through the kind of rapid changes the PR bulbs did. Actually, there was one change to the Magcharger a long, long time ago. The first few thousand Magchargers appear to use a bulb that's sealed at the tip rather than the base (or were otherwise shaped differently.) I've never seen one of these bulbs--I have some lights like that but they all came bulb-less. The sockets don't have a hole for the "tail." Many of these also had plastic lenses before they switched to glass.
Mag didn't used to quantify their light's output, but Streamlight did. Their figures changed over time for a similar 6v halogen flashlight, although I don't know if it was related to bulb changes, improvements in the wiring/battery, or just measuring technique. The SL-20 was advertised as 20,000 candlepower in 1975. By the early '90s the SL-20X was being sold as "up to" 30,000 candlepower with an identical looking bulb. When it was discontinued in 2014 or so it was "up to" 38,000 peak beam candela.