It's more definitive to do an overnight chlorine loss test by seeing the chlorine loss rate overnight by testing after the sun if off the pool in the evening and before it hits the pool in the morning. If your loss is less than 1 ppm FC, especially if 0.5 ppm or lower, then you don't have unusual loss. It doesn't prove you don't have algae, but it's not enough to show up as chlorine demand.

The main downside to a higher CYA level is that IF you get algae or any other reason for needing to shock the pool, it takes a LOT of chlorine to do so.