Was there actually some marking on the Valiant's recorder-marker that said "galactic survey cruiser"? I don't remember that.
My bad. I recall James Blish including that in his adaptation of the episode where he references the ship's name the words "galactic survey cruiser" on the outside of the recorder marker, and yet looking at screencaps you can't see anything other than S.S. Valiant
on the top of the device. I'd always thought Blish was working from earlier script drafts that could have held information that didn't always make it onscreen. I and many other fans have thought this for so long we might have accepted it as self-evident.
That said it does make a measure of sense given the Valiant
being so far out in deep space and then eventually at the galaxy's edge even if it was an accident.