Button Underneath Rear Single Vent on Mid Century Sport Coat - What is its Purpose?

[HQMiner]

Hello all,
About a year ago I purchased this mid century sport coat at an antique store. There really isn't anything special with it in particular. I'm assuming it's from the mid to late 60s due to its overall construction and the height / length of the rear vent.
Which brings us to the main point of this post - the rear vent has a single button placed half way up the right side flap, with a corresponding button hole on the left side flap.

I have scoured the internet here and there over the past year trying to find what the purpose of this button is, but have come up empty handed every time. Maybe I'm not searching the right areas or maybe I'm asking the wrong question, but I've finally decided to enlist this community to hopefully curb my curiousity.

Attached are photos of the front, back, and close ups of the rear vent.

 

[comrade]

Hello all,
About a year ago I purchased this mid century sport coat at an antique store. There really isn't anything special with it in particular. I'm assuming it's from the mid to late 60s due to its overall construction and the height / length of the rear vent.
Which brings us to the main point of this post - the rear vent has a single button placed half way up the right side flap, with a corresponding button hole on the left side flap.

I have scoured the internet here and there over the past year trying to find what the purpose of this button is, but have come up empty handed every time. Maybe I'm not searching the right areas or maybe I'm asking the wrong question, but I've finally decided to enlist this community to hopefully curb my curiousity.

Attached are photos of the front, back, and close ups of the rear vent.

No idea the purpose. It could be from the time, mid-centrury, when button-down shirt collars
came with a button in the back. Here is a post recalling that in 2011:

Back In Action: Brooks Brothers Revives Third Collar Button - Ivy Style

This spring/summer season I noticed a plethora of back buttons on the collars of sport shirts at 346 Madison Avenue. It’s one of those small details from the Ivy heyday that it’s easy to laugh off as a trivial furbelow, until you see how immediately noticeable it is. Like everything in menswear...

www.ivy-style.com

 

[notdos]

I believe it’s to keep the flap closed in windy conditions?