lda #$20; clc; sed; adc #$7a
My emulator gives: A=00, P=2F
Hardware gives: A=00, P=6F
My real Apple IIgs gives A=00, P=7B in both 8-bit native mode and emulation mode, and "mess apple2gs" gives A=00, P=3B so overflow is definitely wrong. And it's not something Nintendo broke even.