The B&H edition I typeset is the so-called "Alte Mozart Ausgabe", made in the 1870-1880s by an unknown editor (my 1978 Dover reprint does not tell who he was). The autograph of this quintet is lost, but my edition lacks any editorial note which states what was the source text. If you are interested in a modern and carefully checked edition of this quintet, search for the Neue Mozart Ausgabe or the Barenreiter Score (the latter is based on the former, but seems to be a little cheaper). You can find it online at http://dme.mozarteum.at (search for the NMA online, VIII/19/Abt. 2, pp. 15-38).

As already said, the autograph is lost; it is therefore difficult to determine what was the original score. In my opinion, some dynamics seem to be arbitrary additions: for instance, this is the only Breitkopf & Haertel score of Mozart chamber music which uses < and > signs to indicate crescendi and decrescendi (usually they use "cresc." and "decresc." only). These signs are often used in a "romantic" way which is not the well-known Mozart style (e.g. mvt. II, bars 30 and 32, clarinet part). I suspect them to have been added by the unknown XIX-century editor.