Hmm interesting question
first of all oral historians cant stand those of a more scientific evidential frame of mind, and get really heated as you are saying that old uncle Jack is a damned liar etc etc
and
formal military dress ( or mess dress) is hardly ever contemporary - so unless they change the dress, dating is hard within 50y.
kinda unlike architeccture.
( kinda also like coins being so imp9ortant in dating archeological strata - sorry that makes sense to me)
so.... the back of the photo may help ( the decoration of the paper it is printed on IS up to date and therefore dateable)
and the style... and
I have 1920 photos of servicemen who are photographed in a woody landscape that you show
interesting question - when can styles date something and when can they not....I wear a rowing blazer and add ons - and intentionally look as tho I have stepped out of the 1860s
Georgian mugs have been made for 200y so if you show womeone one, and ask it is Georgian? they should say hold on I will look at the hallmark .....