No problem - It's an important issue! This data quality issue is called "Point in Time" (PIT).
The short answer is that the data is more than good enough to build strategies on (IMO). The longer answer is complicated. Start by reading:
The topic has been discussed at length on the forum, here are a few relevant threads:
And this:
And (in the same thread):
There are a few ways to stress test strategies if you're worried about this. For example forcing a simulation to only buy stocks that are N weeks after earnings release, or requiring stocks to have had a high ranking system score for multiple weeks in a row before they are bought.