No, it means that you have an unregulated panel and should be running a controller with it
Panels are unregulated but output is temperature sensitive.
If 12v is the nominal rating, 21v out of a 12v panel is fairly normal in a cold clear sunny day like we have been having last week.
In the summer when the sun hits the panels, they will start to drop off as they heat up.
This label is from a 24v 245 watt panel.
It is a 60 cell 24VDC nominal panel that makes max power output at 30.2V but will run up to 37.5 volts if unloaded.