One of the tough things about menswear is that the changes are so small. The width of the lapel wider by 1/4", the cuff of the pants 1/8" narrower, that sort of thing.
And many, many men had there suits made to order, so they kept the details they liked for years after they were out of style.
Some helpful tips:
Button fly is generally 30s and earlier, although they were still worn into the 40s.
Belt loops start in the 20s coexisiting with suspender buttons for some years. By the later 50s, is pretty much belt loops.
Suspender buttons only would more likely be 1930s and back.
Really wide lapels are seen in the very late 30s ,to early 50s. By very late 50s, much narrower lapels and on into the 60s. 60s can be very skinny lapels. Then the wide ones come back in the 70s.
Pleated pants - generally late 1930s - 1940s - 1950s. By late 50s flat : front in to the 70s.
Cuffs - most pants have cuffs of varying widths from the 30s- 50s.
Metal zippers are a must.
Watch pocket set in the waist seam are generally 1950s and back.
Sb jackets will generally by 2-3 button for most of the post Teens period. DB in the 40s is usually a total of 6 buttons, with 2 that fasten. ( 2 over 4) DB in the 80s and 90s is usually 6 or 4 buttons, with only 1 that fastens. (4 over 2)
Back vents - 1920s - 30 - 40 - 50s - no back vent. Then a single CB vent 40s - 50 - 60s. Then the side back double vents 60s- 70s.
I hope this helps,
Hollis
