I'm in Central Arkansas and am seeing newly emerged Poa in shady , thin areas. I am also seeing quite a bit of Bittercress, Henbit and Red Deadnettle emerging as well(mostly in newer customers. We have been spraying for 3+ weeks now and wouldn't do it any other way.
My philosophy on the concept of Pre-emergent is that "Pre" is the key part of the term. By starting a little early, we're more likely to beat the weeds and the leaves. I've been starting earlier for the last 4 or 5 yrs and it works well for us. To each their own.
IMO, if you're in about the same latitude as me and you just started or are about to start applying your Pre-emerg, you are behind the eight ball.
"The Poor Fish" circa 1930's: The Poor Fish wouldn't have been caught if he'd known enough to keep his fool mouth shut.
"Opportunity is missed by most because it is dressed in overalls and looks like work"- Thomas Edison, businessman/inventor