I'm trying to remember exactly what the concern was (this is now probably 20 years back so if it hasn't surfaced it probably never became an issue)... during a few committee meetings there was some discussion about mismatched strengths. Naturally, when one designs a structure, it is anticipated if a failure occurs it should first fail at joint "X." Joint "X" could be defined as a beam to beam, for example. If either the base or the filler is stronger than originally thought, failure may move to joint "Y" which may for example be a beam to column. As I said, this discussion was many, many years (and brain cells) in my past so perhaps no longer a valid issue... or resolved somehow...