Just MHO, but, it is possible your friends are over generalizing and confusing CW period markings with 1873 Springfield type cartouches.
The Arms were marked differently in the two periods.

When they appear, I believe the CW markings are small and usually on the flat wood, opposite the Lock. (Not in the wrist area like a model 1873 Springfield).

Rifling should be Three-Grooves with a slow twist rate of 1 turn in 72 inches.

Dick Hosmer gave you a great clue. Slide one of the barrel-bands forward and make sure the inletting for the band-spring is square-cut and not round at the rear.

(I don't understand this 'Militia' thing. During the CW, the State raised regiments were in Federal Service and were desperately needed.

IMHO - A front line weapon, like a Springfield made in 1864, if issued, would go to soldiers in Federal Service.

There were plenty of secondary weapons to pawn off on the militia, if State militia was even still existing in numbers. Lorenze, Potsdam, obsolete .69 caliber Springfield rifles and smooth-bores were available for such use).

If "the market is soft", that is good for the Buyer (you, unless you are planning a Quick 'flip'), but, not for the Seller. That's the time to Buy!

FWIW - The Springfield, you are looking at, has had the Breech-Plug removed at some time by a 'non-Armorer'. The distorted metal on the right side of the tang shows the wrong type of wrench was used. This blemish is not unusual on original Arms.

photos:
1. The mortise Mr. Hosmer spoke of.
2. My model 1866 - 2nd Allin Conversion has no visible wood markings (except impression/bruise from the impact of a screw-head).

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