Given that few lugged steel frames are made today, I think any lugged steel frame should be 'suitable for discussion'. I've got a bunch and none were made before 1980. My RML is made with a set of 531ST tubing and Everest lugs leftover from the 60s, yet it wouldn't qualify since it was actually built in the mid-80s. My J.P. Weigle, Columbine, and Chris Kvale likewise wouldn't qualify. As I recall, Dale has said before that modern lugged steel frames, handbuilt, qualify, so I think that is good enough for me. Otherwise, I'd say 126mm or narrower rear spacing would be the line of demarcation. Lou