This formula will return an actual date value for the cyymmdd format
including pre y2k. You can format it any way you like once you have
the value.

=IF(LEN(A1)=7,VALUE(CONCATENATE(MID(A1,4,2),"/",RIGHT(A1,2),"/",MID(A1,2,2))),VALUE(CONCATENATE(MID(A1,3,2), "/",RIGHT(A1,2),"/",LEFT(A1,2))))