I always enjoy these discussions as it's been a long time since the 97 cutoff point was introduced.
1997 still makes sense as a time when technology made a significant change.
I am starting to see the period around 2009 being another important time and end of an era. My 09 Yeti ASR has 26" wheels, 1 1/8 headtube, 100mm/135mm Q/R hubs, 25.4mm bar, threaded BB, 9spd drivetrain, seatpost that doesn't move unless I get out an allen key. My memory is blurry over the next few years as standards started to change but this was the tipping point.