I would avoid getting extremely specific with rules for years and number of starts and just say in general that it is important to understand that the max possible effort for a horse changes over time. Every horse is different, though some sires tend to have somewhat predictable patterns.

The key to finding value is understanding when the max possible effort for a horse could be improving and it hasn't run to that max yet. Some horses can only run their best at 2 and then tail off at 3 or 4 (assuming they are still running). Some horses run their best at 3 and never get back to it. Some are good for many years. Some dont get good until 4 or sometimes even 5.

As always, there is an exception to every rule, but in general yes you want to see an indication that this year's numbers are going to be as good as last year's best within 2 or 3 races. Regardless of what year we are talking about. When they haven't gotten back to it, good chance this is the beginning of a "tailing off" year for that horse.