The organbook of Matthias Rottenau (Mus. Ms. 40615 from the Staatsbibliothek zu Berlin) contains numerous works from unnamed composers. All the works contained are sorted by category. First come all the preludes (Preambuli), than Introiti, Toccate, Canzoni, Capricci and finally the Ricercari. The first bunch of pieces in each section is preceded by a nicely drawn Initial, giving the title of the piece, the tonus and (thoug not always) the composer. The last bunch of pieces in each section go without initial, though space is left open where one could be drawn in. So it's only a supposition that the pieces wihout initial that follow for example, the Ricercari with initial, are Ricercari as well.
This one of those Ricercari. It's actually wihout title, without tonus and without composer. but for now I designate it as a Ricercar, secundi toni. If someone knows for certain that's correct or not, I'd like to hear it.
Score available here: http://partitura.org/index.php/anonymus-ricercar-secundi-toni-2/