AC recharge 91 nsx help. R-134A

[KraftwerkTurbo]

I'm not EPA certified or anything like that but here's what I did.

My original R12 system stopped working.
So I took the NSX to the dealer and had my R12 system purged to remove any R12 remaining.
Then I bought and installed the Honda OEM r134a retrofit kit.
Then I had the dealer test the system for leaks.
No leaks were found.
Then the R134a from the retrofit kit was added following the Honda instructions.
My A/C works fine now.

Stored for future reference.
Plus adder "changed my o-rings to the new, green ones just to be sure as mine are original from 1992, and a new filter/drier while the system was empty."

Any tips how to determine if a car (1991) has been converted?
A) check how the high/low pressure ports look like. If newer style, indicates car has been converted
B) sticker under hood

If in doubt: evacuate the system, get R134a retrofit kit and perform above?