If the rating was determined in 2017, you can expect the difficulty to resemble what you find in the gym. It's the 5.9's whose ratings were applied in 1975--back when there was no such thing as a 5.13--they will kick your ass because that 9 is a 9/10, not a 9/15c. We've been making the denominator bigger as we continue to invent harder grades, and it creates a skew problem.

While this is mostly true, I just want to point out that it's mostly the less traveled routes that have this problem. Someone with a modicum of crack technique and an unremarkable gym ability will be able to get up Nutcracker (famous old school Yosemite 5.9 climb) without it feeling like they're doing anything above gym 5.10.

Good to know, thanks.

A member of my crew likes to seek out off-the-beaten-path climbs. The rest of us are just happy that somebody has a plan. Maybe this has set me up with a bit of a bias.