The Vegagerðin map is, as best I can tell, a quite reliable source
for what they maintain. This is not 1:1 with what is signed, since some routes are not signed (or only partially signed), and others are signed across locally maintained streets. And... yes, in some cases there are signed routes that are completely absent from the map (meaning the national government does not maintain any of it).
The general guiding principle is that signage is the final arbiter, though. Ergo, I would want to see confirmation that signs have changed before doing anything with either of these routes.
(FWIW Mapilarry does also have
imagery from 2019 showing 431 still there)
