Many interesting thoughts here -- all of which makes one leery of
any pitch raising (half written in humor -- or written in half-humor)!
I did think of one question to ask those who have had this happen.
Was any observation made of the breaks where one could see signs of an
old break (rust in the break itself, or other signs of the break being
exposed for a long period of time)?  Fresh breaks in metal are pretty
easy to identify, as the metal should be shiny-bright within the break.
Also, any voids in the metal within the break?

Did any piano maker use cast steel for the plate?  Or ductile iron,
both of which would be much more durable when flexed.

As in the ad, "Inquiring minds want to know!"

David Dewey