theres a safety margin in the manufacturers determination of redline
my experience
first bike, honda super 90, bought it used for like $50 it was a turd, every other kid in town owned it before I did. I had it about 2 months, no tach, but my bet is 80mph was faster than it was designed to go, but with a long relatively steep downgrade it would, till I heard a ticking noise, I just couldn't give it enuf fuel, it was thursty, so it began to eat solid food, valves, heads broke off, I tore it down, they were like marbles inside
later in life, I had a Honda cb125s, I passed it on to my eldest son, withing a month it suffered the same fate as the S90
move on, my 1982 Yamaha XV920R, no rev limiter, easily pulls 1500 past redline and still wants to pull, don't do it a lot, but occasionally, 60k no issues yet
and finally, my 99 SV650, (gp shift)I admit, I have occasional brain farts, first one is I pull on to a nice stretch of open road, not a car in sight, time to practice a 1/4 mile run 1st gear to redline, click down into second, bring to redline and have second brain fart, ferget ya got gp shift, click back up into 1st, yes, shift into 1st at 70mph+ on a SV650, I'm sure I saw the tach past 13k maybe more the first time was not for long, I got clutch pulled in,
second time, a year or more later, I was really spaced out for some reason, did almost the same thing, but never pulled the clutch in, I just rode out the skidding rear tire till the engine speed and tire speed matched, again it was over 13k for more than a split second though, as many as 10 seconds (on an engine with over 90k)
ooh also a cage I used to regularly abuse, an '82 BMW 320i (e21) I loved to drift it on cloverleafs 500-1000 over redline, still ran strong with 460k original motor when it was rearended and totaled
, it was funnest car I ever had