There were no SAMMI standards in 1875. There is wide variation in the shoulder configuration of the chambers of different firearms. In other words, the brass will have different shoulder shapes depending on which gun it was fired in. My pistols and rifles in 38-40 leave the brass in all sorts of configurations.
But, your question is about reloading. And, here too, the absence of SAMMI standards for 38-40 result in shoulder shapes that vary widely from one die manufacturer to another.
You don't have a problem at the present time, as your brass goes back into your one, and only firearm in 38-40. But, that will not be the situation in the future as you add new guns in this caliber.
I have three sets of 38-40 dies. Hornady, Redding, and RCBS. The only one of the three that sets the shoulder back far enough to work in ALL of my guns is the Hornady. Often people report that the RCBS dies can be made to work by taking material off of the base of the sizing die, thus affecting the position of the shoulder by being able to run the brass further into the die. I've not done this personally, but have done it with RCBS dies in .357 sig successfully.
So, your future guns will tell you what you need to do with respect to resizing 38-40.