I consider climbing down to a rest or the ground still part of the first try...and its always been considered that way, in my memory...shoot, half of the reported onsights in literature involved downclimbing to rests or back to belay ledges...
And, FYI, onsight used to mean a description of the style the route was climbed in! and it meant no rehersal and no prior info/beta...it was only when it was combined w/ the word "flash"...as in "onsight flashed", that it meant a no-fall first try ascent...in fact, there was a huge description of a route that scott franklin did where he reported climbing it onsight, the mags report that and implied a no falls ascent, to which he wrote a letter back stating that, while he had climbed the route "onsight" he had fallen twice...get yer facts straight
Now, the term "onsight" has evolved much the same as the term redpoint has...onsight is now inclusive of a flash...