Vintage chocolate trench coat

This trench coat has no size tag but measures 17 inches across the shoulders with a length of 45 in. Sleeve 22 in. It is in like new condition. The inside has buttons up both sides and around the back collar. I'm not sure what the purpose of these is? Maybe there had been a liner at one time that you could add. There is an inside pocket as well as two outside pockets and a belt with a kick pleat measuring 22 in. This coat fit me well and I'm a size 16