Yes, that is indeed likely. I was not too worried about the missing rosette in the breast shield either, until I saw it in combination with the crown. A count would normally not have used a crown at all (it may have been granted as a privilege). The Callenberg arms you found uses a triple crowned helmet as a helmet sign, using a duke's crown. Helmet signs and mantles do not have the same status as crowns. They are more like decorations. Motto and supporters have a somewhat higher status, but they can be left out also. The part that counts (pun unintended) are the arms themselves and if they are covered by a crown, it is part of the arms. The crown used on the piece is an elector's crown, far above the station of a mere count.
The Von Callenberg dynasty died out in 1850, when Clementine Kunigunde Charlotte Olympia Louise, Gräfin von Callenberg died. She was married to Ludwig Carl Hans Erdmann von Pückler, Graf von Pückler, Freiherr von Groditz, who did not inherit the Callenberg title, but used Pückler Muskau instead. Therefore, the arms were void after 1850. This may have been the reason they were used on the piece. The crown and rosette may have been commercial changes or they may have been a built-in defence against anyone still wanting to prevent spurious use of the arms or both.
Peter
