The oval buckles came out so that there were no longer any sharp corners, and the details on the buckle made it so that the buckle didn't require polishing.
I would warn other collectors that it is a good idea to spend a lot of time looking at the details of the jackets and making your own conclusions rather than simply taking other collectors' words for it when discussing originality etc.
Wartime buckles were usually rectangular plain brass, while post-war ones have a rounded buckle with a textured design.
Sorry, but I have to seriously disagree with this assessment.
There are three different variations of the Dress uniform: Evening Dress, Blue Dress, and Blue-White Dress; only officers and staff non-commissioned officers (SNCOs) are authorized to wear the Evening Dress. This uniform has since been replaced with the Blue/White Dress uniform for officers and SNCOs.
Officers, NCOs, and SNCOs wear a scarlet stripe down the outer seam of each leg of the blue trousers.
As you stated, the easiest way is with a dated tag.... The stripe around the cuff sounds like an indication that it's an officer's grade uniform....
Bodes Assuming we are talking about the officer's dress uniform, the buckle on the waist belt can help date the uniform.
It is interesting that the first blouse (navigator) doesn't have the seams above the pockets, though it has a square buckle.
Since officers' uniforms were privately purchased, they are commonly found to be custom tailored which could account for the lack of the chest seams.