senza sord. is one of the abbreviations that carries more than one meaning. Written out, it can be senza sordino or senza sordino — 2 separate directions that happen to shorten to the same letters. The score itself decides which: the surrounding passage, the instrument, and what the music is doing at that moment.
senza sord.
In a score, senza sord. can stand for senza sordino or senza sordino. Here is how to tell them apart.