Nikki added a comment. We already have Norman under the (completely incorrect) code nrm and T25216 is asking for the existing Norman Wikipedia to be moved from that code to nrf. If that happens, I would expect Wikidata to also switch to using nrf for Norman. nrf explicitly covers both Jèrriais and Guernésiais and possibly applies to the other mutually intelligible varieties too (might be worth asking the ISO 639-3 RA for clarification). Either way, if you specifically want to say Guernésiais, I would suggest nrf-gg (i.e. including the country code for Guernsey) as a more appropriate code (and then Jèrriais would be nrf-je).
TASK DETAILEMAIL PREFERENCESTo: Nikki
Cc: Nikki, jhsoby, GerardM, Baba_Tabita, Aklapper, Esc3300, GoranSMilovanovic, QZanden, Izno, Wikidata-bugs, aude, Mbch331