Just trying to help, but don't blame me if my advice is useless. I am by no means a specialist or have any clear idea about old military equipment.
An idea would be to compare the fabric with other period pieces that you can clearly place in time. The leather would look the same (leathering techniques should not differ that much over those years), but maybe the fabric (texture) and maybe the metal parts are sufficiently different to help identify a year.
Of course finding a photo with a soldier carrying it would be ideal. Good luck with it!