Dr_Quark:
Fortunately, the one bad display that I've reported to the vendor also had a bad solder connection that has to be pressed on to work.
I've seen issues like that before.
A quick touch up with a soldering iron should fix the issue.
I've seen cases where the PCF8474 chip had poor soldering and some pins were not making contact with the solder pad.
I'll see if I can get the other 3 to function with new code.
I'd recommend first running the I2CexpDiag diagnostic sketch to test them.
--- bill