Latest dope on R12 to R134 conversions - experience?

I have a license for buying R12 but I am considering changing over my A2
with the retrofit kit.

Obviously, prudence says to change the receiver-dryer and remove and flush
the system for a perfect changeover perhaps using the PAG oil BUT:

I spoke to a local discount auto parts manager who said "last year I topped
up with a can of R12 but this year in one of my old cars I simply used the
retro-fit kit and the A/C works fine." He did not change anything. (as the
kit says is not necessary) I have read failures on compressors without
doing a complete changeover (new receiver/dryer and flushing changing oil)

The retrofit kit contains Ester oil <spelling?> that is more compatible with
the R12 oil.

Has ANYONE, long term, used the retrofit kit only WITHOUT changing the
receiving/dryer and flushing, just using the kit with NO problems?

Harry