Good research on designations. I always found the alphabet soup of Navy aircraft designations perplexing.
Where as Army/Air Force P-26, P-40, P-47, B-24, B-25, B-26 type designations made sense to me.
So I contrived PBH-417 this way (if you missed it)
PB > Patrol Bomber works for PBY PBM
H-4 > Hughs H-4 core model of build
17 > Lotz of B-17 content