HI has a lot of unsigned shorter state routes, especially 4-digit routes near military bases on Oahu. HIDOT assigns a route number to every road its Highway Division maintains, even the ones not relevant to most travelers. Our usual policy of ignoring unsigned routes comes in handy there, even if it means leaving out an unsigned primary route like HI 95 in southwest Oahu.
Complicating things even more is that there are a lot of county highways signed exactly like the state routes. OSM incorrectly labels at least some county routes as HI ___. There are also a fair number of poorly- or un-signed numbered county routes, especially in central Maui.
BTW, HIDOT told me it was going to sign the newly-completed HI 3800 Airport Access Road in Kahului, and so I went ahead and added it to the HB. Did you see such signage?