Found this amazing image in a book yesterday and fell in love instantly. It's by the workshop of Bernardo Daddi and dated to 1334. This is a donor.
I mean: Look at the fabric! And the side and front slits. yes, there appears ot be a front slit too. It is the lining, probably fur that we see at the side and front slit, the tunic worn under the surcoat is, like in most of the images, made from the same fabric as the surcoat.
But this surcoat has a front slit! And side slits, but as I've discused previously in the blog, they are common.
Front slits are less common, but I've found a few:
This surcoat, painted, by Giovanni Baronzino, may also have both side and front slits, if you look closely at the front.
And the saint to the right in the yellow gown, on this painting by Paolo Veneziano.