Consolidated model and preliminary design designations

[airman]

The XPB3Y-1 (model 34) was the prototype of a long range flying boat for patrol and bombardment missions. A single example was ordered in April 1942 with serial 32386 but was subsequently cancelled in November 1942. However, John Wegg, in General Dynamics Aircraft, also lists it as model 30.

Jos Heyman

i have found more in this pdf about XPB3Y-1.

 

[overscan (PaulMM)]

So known preliminary design sequences are

BC - Boat Commercial
BM - Boat Military
LB - Land Bomber
LC - Land Commercial
LO - Land Observation
SC - Seaplane Commercial

 

[Stargazer]

The Model 15 Courier was a Pratt & Whitney-powered experimental commercial variant but only a prototype was completed.
Source: Putnam's "General Dynamics Aircraft and their predecessors" by John Wegg.
In my opinion, the XO-17A is not Model 15, but a Model 2.

You are absolutely right about the Model 15, and I also concur with your opinion on the XO-17A.