"A" and "B" ends NORMALLY are used only on non powered rail units to designate which end has the hand brake mechanism. There are exceptions to every rule but by in large, the "A" end has the hand brake wheel at it. Any locomotives with the A and B marking should follow this premise. On multi-unit stack cars, then they go A,B,C,D, etc but still hold true with A being the hand brake end.
With regards to NS, the majority of all high hood units were built with the operator console on the left hand side or with dual controls to run long hood forward. By the 1980's when the high hoods and dual control stands became too expensive, NS began getting low short hoods with the control stand on the right hand side but the stand was "kicked around" a bit from standard and USUALLY the unit had two speed indicators so that in either direction the engineer had an unobstructed view of it. The last GP60's for NS were set up this way but the short hood is considered the front. With the wide cabs and desk top controllers obviously the point became moot.
With both new builders returning to "standard" control stand instead of the desk top, I would not be surprised to see dual speed indicators showing up soon. NS is requesting demo units from GE and EMD with the "old" control stand but the short hood will still be considered "front".
The main proponents of long hood first on NS (and predecessors) for safety reasons are now pretty much all retired. I will give NS credit though as their wisdom in setting up units to run equally well from an operator standpoint in either direction surely saves them a lot of spinning and wye-ing units. Spinning/wying is a major bottleneck and non revenue problem with railroads.