Let's say Value Line upgrades XYZ Corporation from a timeliness rating of 3 to a 1. Most subscribers learn of this upgrade when the service arrives on a Monday. The price of XYZ stock printed in the service, however, is from some time in the previous week. This increases the demand for shares. And since the price of a stock at any given moment is determined by supply and demand at that time, the tendency can be for the stock to increase in price compared to the price that was printed in the Value Line service the previous week.
Demand goes up, price goes up.
When the timeliness rating is lowered at some date in the future, the opposite could take place. Demand goes down, price goes down. As I said, I tend to find more comfort in trying to focus on fundamentals like growth and profitability rather than whether the tide is going in or out on price momentum. Please don't get me wrong. I'm not knocking Value Line.