Romance was probably written between 1811 and 1821, when Weber rested
from opera, if indeed the piece is genuinely by Weber. There seems to be
no hard evidence from any contemporary source that it is by him, but
since it first appeared with Weber's name at the top around the beginning
of the 20th century no other composer has been found to replace it.
Trombonists of course are woefully lacking in works by the great classical
and romantic composers, so they have never thought it worthwhile to
abandon this piece, even if its origins are questionable.