After training in Driver Ability one of his attributes (can't remember which) increased by one and that caused his overall rating to jump from 15 to 17 which is two above my manager level. How did this happen?
Likely his overall rating was just out of sync and from the old iGP, not a big issue.
When I level-capped drivers and staff we allowed teams with those who were 3 levels or less higher than the manager level to keep their levels. It was only extreme examples of 4 levels + higher than the manager that were capped. As this doesn't breach that rule, I'm happy for you to keep the driver.
This also answers my previous question about a L16 manager in our league who has a L20 CD. The difference being that a L20 CD has a huge influence on initial car design but I know you're also addressing this so well done and thank you to you and the team for all your hard work.