"If genuine, and he did not data-mine the parameters after the 1970s discovery"

That is open to debate. The 2 people who can answer this question about long term effectiveness are Robbie and Zee.

There are many variations of Breadth Thrust - this falls into this class.

Essentially the BAM indicator is a Pooled Ratio of Advances/Total >67% cumulated over 10 days. Question is it can be done on Issues and/or Volume. Which one?

The classical Zweig Breadth Thrust is long term backtested ..... It has iirc never failed to mark the initiation of a Bull ... while on the other hand it DOESNT purport to being 100% accurate - like this one. 100% accuracy tends to be a bit fallacious - and brings on the Data Tuning questions.

NOTE: This one doesn't trigger in the 2002-03 Bear end.... which makes this a bit suspect.

The classical ZBT did not trigger on this rally - because it has an Oversold requirement (<40) and then rise to 60 over 10day period.
BUT - if you relax it a bit ...ie not require <40 but require the 20 point rise

it did trigger on 1/12/2023 - from a low of about 43 on 12/28 to high of 67 on 1/12.

Concept is the same : You HOLD 1-3 months out and Indices are higher

Hope it helps!

Best