I'm not sure how far back you're referring to, but I do indeed have an older pair of DT770s (the ones that say "professional" on the headband sides). It's from the mid-90s I suspect. In fact, just this week I heard back from Beyerdynamic about the history of the pair I have. Apparently the 770 line began in the 80s simply as a 600Ω headphone. This continued until the late 90s when the driver was replaced with a 250Ω version. I believe it was later on that this headphone was split into Pro and Premium varieties.
As for comparison, I can only comment on what I do/have own/owned: DT770 600Ω (circa 1995), DT770 600Ω, and DT770 Pro LE. Neither of the new ones sound as good as the old pair. I was disappointed in both, to be honest, because I was hoping they would replace this old pair. But, no go. Not good enough. Really, even out of my iPhone these old 600Ω cans have fuller bass than the 32Ω Pro LEs. Go figure.
strange, but I like the Mad Dog atm as a closed dt 880 compliment actually!