my late-2013 15" mbp upgraded with no issues, but I do recall reading prior to I stalling and noting that any older, or smaller model of that age was not suppo

my late-2013 15" mbp upgraded with no issues, but I do recall reading prior to I stalling and noting that any older, or smaller model of that age was not supported. most of the reports I've read seem ti concern the smaller model and I'm left wondering what did they expect?