Hi JimJ;

I have no question your joweled plate is an addition. This type of joint is typical of additions. Two other pieces of evidence are some weather marks showing the old vertical boarding and the rafter overhangs the tie beam an inch which is a way to lap the gable boards over the lower wall boards. Nice barn.

Jim D.

The closer you look the more you see.
"Heavy timber framing is not a lost art" Fred Hodgson, 1909