Your CYA was significantly higher than 90 in the first place if the drain resulted in 80. The test isn't as accurate above 100ppm, so that makes sense if you're sure of 80 right now. You're getting practice with the test, so I'm inclined to believe the 80 is a good number.
That being said, and yes it's a PITA to do again... 80 is going to be difficult to manage this season and there's still much of it left. I'd recommend trying to get closer to 40-50 if you would like to use less chlorine and decrease your stress level over the pool this summer. One of the side effects of BBB the TFP way is a bit of stress and obsession over water chemistry and if it's off, an immediate desire to drop everything and shirk your responsibilities so you can go nurse your pool back to perfection :~} You can save yourself some of that downside with a lower CYA level. Plus, it'll mean a week on vacation with a floater and a couple trichlor pucks won't wonk your pool much either.
That being said, and yes it's a PITA to do again... 80 is going to be difficult to manage this season and there's still much of it left. I'd recommend trying to get closer to 40-50 if you would like to use less chlorine and decrease your stress level over the pool this summer. One of the side effects of BBB the TFP way is a bit of stress and obsession over water chemistry and if it's off, an immediate desire to drop everything and shirk your responsibilities so you can go nurse your pool back to perfection :~} You can save yourself some of that downside with a lower CYA level. Plus, it'll mean a week on vacation with a floater and a couple trichlor pucks won't wonk your pool much either.