I am not a guru, however, I have a mag with multiple stamps, and a mag with only electro stencil. They have identical bodies, but different sliders inside. I'd assume that the makings only happen during re-arsenal, and stamp vs stencil would depend on which arsenal did it.
I doubt that original magazines were ever marked to match the rifle.
For what it's worth, both official Soviet SVT-40 Field Manual (1940) and SVT-40 Repair manual (1942) explicitly specify that each magazine shall have a number matching to the rifle.
The Field manual says "When inspecting the rifle, check that: 1) numbers match on the receiver, trigger guard, bolt, stock, magazines, and bayonet." Note that the check for the matching numbers is listed as the 1st check (the other checks are mechanical and function checks).
The repair manual says "Serial number shall be on the receiver, bolt, bolt carrier, trigger guard, stock, magazines and the bayonet. These parts are fit individually to each rifle, and their numbers shall match."
Note that both manuals say "the magazines" in plural (not "the magazine").
Both manuals don't specify the number of magazines issued with each rifle, but the Field manual says in one place: "Each soldier must always leave one full magazine as untouchable reserve, spending of which is only allowed with the commander's permission". So it must have been at least two magazines per rifle.