> If a stock goes up 20% in a year, the market might have undervalued it last year, or is overvaluing it this year. It's unlikely the it was correctly valuing it at both times. In the absence of a Covid-19 pandemic, act of god, etc. of course.

Or the company has grown its revenue by 20% in 1 year which isn't necessarily unheard of. Or they significantly beat the expectations of analysts / their own guidance. In all of those cases the stock could have been correctly valued & still experienced growth.