I typically attribute a few things to people that make huge gains within a season and that is:
If they’re coming off a long to short, and its at the shortest end of the spectrum, or short to long and its on the long end of the spectrum. I’m never surprised to see my 200m time drop by 0.5s between two races.
If their plan was pretty much a waste of time or poorly planned, then the intensity of competition will provide gains within itself. For example a guy who runs cross country all year and then goes and runs 100m sprints. Well their body will adapt to those 100m pretty quickly but also stall quickly and the chance of injury is quite high.
Someone who trains through competitions and only tapers later in the season will probably have a pretty dramatic time drop during the season. I would never underestimate the power of a good taper.
Proper planning cannot be avoided if you want to maximize your potential. In each of those scenarios I believe that a person will run their fastest times if all things are in check prior to competing.
I’m never going to run my fastest 200m possible if I keep leaving competitions take care of that aspect of my race. The last situation is probably the best option in terms of development when necessary.
Great talent is sometimes lost in poor planning, and you’ll see glimpses of it when their going through competition periods.