1970s Design Indulgence

Some things maybe, but in the transition from valves to transistors there must have been some misunderstandings. An example being Dinsdale's admission that he'd not considered the heavier ground current, which he found to be a problem when converting his amp to stereo. You can see the same in the Quad 303 (R115), and also the use of a regulated supply. Decca research "solved" the grounding problem, but not as completely as Ed Cherry saw it. Even Doug Self made the comment that after 40 years of amplifier development, nobody could claim it perfected.

There were solutions for the unmeasurable from John Linsley Hood, who was sometimes lambasted in letters to the (WW) editor, but Mr Vereker took note and it did well for him. I'm pretty sure everybody was learning, and not just from measurements. Then there is the discredited Matti Otala and his "overshoot" explanation. I still think he was right in some ways, just that he presented the "proof" with shaky evidence. I don't think anybody can claim to fully understand everything about amplifiers, simply because we can't measure the thing it's supposed to do - the music.

Obvious faults were not all that obvious for the designers of the day, and you can see how I've missed plenty over the last 150 plus pages. Learning is an upward spiral where we often coming back to a previously discarded solution, finding it useful next time, because the reasons gradually reveal themselves.

Op-amp similarities with modern power amplifiers firmly shoved earlier circuits out of the way. And I guess the reason was, as you suggest, to curtail development time when things got too problematic. Even so, designers like Bob Cordell have developed the mathematics which also work to analyse and correct these older designs - in many cases allowing simple calculator sums with which the simulator agrees.

Even with seemingly endless development time, we cannot give every answer, and I think the Radford - Bailey story is just one of many to show that. We can only conjecture that if it works, it works like this... until we discover otherwise.