There is quite a few inter-railroad letters in the SRHA archives but I don’t recall anything between the Southern and the Northern Pacific. The Southern was constantly experimenting and proposing design changes to EMD. EMD may have passed an idea along to, or from, the NP.
I am certainly not saying any published material is wrong, esp if written by Warren Calloway, Tom Sink or Paul Withers. Unfortunately, we see a lot of "conventional wisdom" that may not be absolutely correct, I’d like to see more documentation or specifics on some topics.
My main reason for questioning the use of our mysterious hatch for ventilation is because of documentation by EMD. “Product Development” sheets for F-7s and E-8s (attached) discuss “pressurized ventilation” and “into the engine room under pressure”. (Both pages were issued January, 1949.) If those designs were faulty, I would expect us to see modifications of some sort on multiple locomotives?
The answer here may simply be “as far as is known…..” I suggest we can accept that where an absolute answer cannot be found when we realize how much material (answers) has been preserved in archives donations from NS and the Marvin Black collection.