I have always thought of the bridge patch and the bridge brace (which passes under the fan braces unlike the Bouchet bar) as being the same thing even though the patch is short, low and wide while the brace is long, not quite so low and as thin as a fan brace. In a presentation by Daniel Friederich in 1998 he seems to have the same opinion as he mentions both as ways to “consolidate and stabilize” the arch of the guitar. http://www.orfeomagazine.fr/documents/Soundboards_DF.pdf The other advantage I see is that it makes glueing the bridge on much more reliable when using traditional methods. Not to mention avoiding cracks at the bridge ends. 

Ever since I have used these elements in my guitars I have wondered who was the first maker to do so. The oldest bridge patch I had ever seen was on a Hauser and again Friederich in the same article says, “Used first by Hermann Hauser I in the first half of this century (around 1930)” The funny thing is that in talking about asymmetry in the same article he shows a drawing of asymmetrical bracing on a guitar (c. 1850) made by Mirecourt-trained A. A. Chevrier  (later of Brussels) which shows a bridge patch. The information comes from Dominique Field.