Inset you serial number from your console
TL;DR. Compare your serial here to know if your Switch is patched or not:
Serials beginning with XAW1:
Serials between XAW10000000000 - XAW10074000000 are safe to buy
Serials between XAW10075000000 - XAW10120000000 are possibly patched
Serials above XAW10120000000 are definitely patched
Serials beginning with XAW4:
Serials between XAW40000000000 - XAW40011000000 are safe to buy
Serials between XAW40011000000 - XAW40012000000 are possibly patched
Serials above XAW40012000000 are definitely patched
Serials beginning with XAW7:
Serials between XAW70000000000 - XAW70017800000 are safe to buy
Serials between XAW70017800000 - XAW70030000000 are possibly patched
Serials above XAW70030000000 are definitely patched
Serials beginning with XAJ1:
Serials between XAJ10000000000 - XAJ10020000000 are safe to buy
Serials between XAJ10020000000 - XAJ10030000000 are possibly patched
Serials above XAJ10030000000 are definitely patched
Serials beginning with XAJ4:
Serials between XAJ40000000000 - XAJ40046000000 are safe to buy
Serials between XAJ40046000000 - XAJ40060000000 are possibly patched
Serials above XAJ40060000000 are definitely patched
Serials beginning with XAJ7:
Serials between XAJ70000000000 - XAJ70040000000 are safe to buy
Serials between XAJ70040000000 - XAJ70050000000 are possibly patched
Serials above XAJ70050000000 and above definitely patched
Serials beginning with XAW9:
Refurbished Consoles directly from Nintendo, no informations, but
very possible all patched.
Serials beginning with XAK:
No informations available, since those are only sold in Korea (?)