Son began HS as a 2017. Had great success in his foreign language class. Won substantial scholarship opportunity to spend junior year living abroad, studying and living with a host family. He was just getting into a rhythm with his baseball and basketball recruitment. Had made several visits to Power-5s fall of sophomore year for both sports.
Was torn about what to do. Did not want to forfeit the all important junior year of HS sports and the momentum of his recruitment, but also knew that if he was to play hoops or baseball in college, which was the plan, he'd never be able to spend a year abroad, much less a semester. The obvious detractor would be the loss of physical and skills development in baseball at such a crucial time in his life. If he were to take the opportunity it would, in effect, mean eleven straight months of ZERO baseball, at age 16-17, a time most would call the pinnacle of HS baseball development and college recruitment.
By March of sophomore year he finally decided to go only after we learned he could do a PG year (Post-Grad Year) after he graduated with his class in 2017, and would allow him to have that 4th year of HS basketball and baseball that he'd be forfeiting by living abroad junior year. And by doing so regain the time to catch back up on any skills and development lost while abroad, and the time to re-enter the recruiting marketplace.
Son would NEVER trade his year abroad for anything. It changed his life. But there have been many, many unintended consequences as result of the unconventional path he chose. And not all good. To loop this back around to OP, it is however the very reason why he is doing a PG year now, and in effect "reclassifying" to the 2018 class by doing so.