These BSC marked 37s were loaded by Bethlehem Steel Corps. They were made by other factories. The one with a W in a circle was loaded by Winchester. Poole cases and projectiles are quite common. The over laping contracts for ammunition companies is a study in its own right. A company may have a production contract with a government or other company but NOT a LOADED ammunition contract. Most of this is political at the top. A company may have a contract to LOAD for export but not their own ordnance. Why? The Defense department has as its prime mission the filling or orders for the US military. A certain company may have an ability to make more ordnance than they can load and so the overage goes to another loader. Similarly a company may not have enough capacity to load as much as they can make and farms out the overage. Plenty of reasons for ammo to end up with 2 headstamps from different companies.
Bethlehem steel was a huge company in this era and although they did make smaller shells ( 37mm size) they were far more interested in making big ones. The company was far larger than Poole or UMC or Winchester. They had huge contracts from all over the world for ordnance including a massive contract for 76mm shells for the Czar of Russia much of which they were stuck with when the revolution broke out.
One of my presentation shells was given to the Imperial Russian ordnance inspector who was resident at BSC after a certain huge number of shells were made. Like many Imperial Russian officers he sayed here when the revolution broke out. No long term opportuities for Czarist officers in the new government.
Ordnance contracts can drive you nuts trying to figure out who and why,
Consider today , for instance , you have a British arsenal making ammo for a German gun company for submission to the US for testing. This is nothing new. These arrangements only break down during war and sometimes not then.
In these cases BSC may have offered a better price for the loading and delivery of these items since they were working with a much greater economy of scale. They were selling ordnance by the ship load.