I have noticed that old Gen Bb’s have a different mouthpiece than the new ones. I’d like to know when did Generation altered the design of their Bb’s. One very noticeable difference from the old and new mouthpiece design is the vertical line above the fipple hole. (To those who have an old Gen Bb, have you noticed that too?) Please do tell me the details. thanks 
I’m not sure exactly when the whistle head design was changed,but I have brass ‘redtop’ whistles in Bb and also D,which I purchased in the early 80’s.
These older Generations are often thought to be better than the later models,though apparently there has recently improvement in overall quality reported.
I remember that the Bb needed a bit of fine tweaking of the blade,but it is now a fine characterful whistle.The D only required the head loosening and the ‘Bluetack’ tweak to produce a great instrument-it’s one of my favourites.
PM or Email Jerry Freeman on this. He is the expert in Generation whistles after having tweeked quite a few. He told me the mouthpieces changed in the early '80s and that most whistle players want the pre-80’s whistle with the ridge running down the top of the mouthpiece.
The closest I’ve been able to date the change to the new Generation whistleheads is early 1980’s.
It’s hard to pinpoint because the older ones continued to be seen in shops for quite a few years after that. My guess comes from talking to people who remember approximately when they first began to see the new ones in shops.
There were changes in the whistlehead geometry that did change the voicing somewhat and make the newer Generations, as a group, less consistently easy to play cleanly than the older ones (more buzzes, rattles and squawks, fragile low notes). Because of the difference in voicing, the older Generations tend to be slightly sweeter sounding. (These are two different issues – voicing and playability – and there are different aspects of the whistlehead geometry that changed, responsible for each.)
Even among the older ones, though, you still had to cherry pick the best ones, although good ones were easier to find. And there were periods of poor quality with the old ones, too. Someone told me there were a few years in the '70’s when they were consistently bad, and then they sorted out the quality problems and got good again.
And you are correct, the ridge along the top of the beak (like the ridge of a roof) is the easiest way to recognise a pre-1980’s Generation.
Best wishes,
Jerry