The answer to that question is up to the user and the grounds staff. Here are two photos taken on Thursday and Friday this week. The first photo is from the Colts Training Camp fields in Anderson, IN at Anderson University. This was not overseeded in the fall.
The greener plants in the upper left of the photo are some "volunteer" annual ryegrass. This field will be cleaned up with a Katana spray in the next 7 days.
Next, a photo of the Colts practice facility field at the Colts Complex off of west 56th St.
This Patriot bermudagrass field was overseeded with Barenbrug Turf Star Elite Ryegrass at a rate of 20 lbs per 1,000 sq ft. The ryegrass overseeding will stay until the completion of mini-camp in mid June. At that time, a Revolver application will be applied and then it is back to bermuda and growing the field in for the start of practice after the conclusion of training camp.
So, overseeding is up to the end user and the grounds staff. Both fields are playable, but one is obviously a bit greener.
Go to j-dturf.com to learn more about J&D Turf.