A network for historic guitars and vihuelas
GiovanniSmit4courseguitars.jpg There are apparently two surviving 4-course guitars but they date from the 1640s. They were made Giovanni Smit. One of them is illustrated in James Tyler's book The guitar and its music p.82.
There is the Belchior Dias guitar: here, which is generally considered a renaissance guitar although it has five courses.
Also, there are fragments of a four course guitar found in a ship wreck, but from ca. 1733 so not 'renaissance' in any way. There was an article about this in Lute News 131, October 2019.
So, maybe we should examine what we mean by 'baroque' :-) ?
My guess would be the Dias!