Good point Kootoo,
For Spring Seeding, its actually a good thing to plant it in november or so. Seeds like the cold and the snow to get prepared for germination.
The reason people are looking to get it planted by a certain time, september 15 ideally in SE Michigan, is so that the seedlings will be strong enough to survive the winter. If you plant so that seedling come up too close to winter you can lose a lot of it.
On the other hand if you are past that time, skip some time until right before winter to put your seed down. Unlike seedlings, seed actually will benefit from the winter. Though you may risk losing some to erosion and birds and such until it germinates in the spring.
well thats just my 2 cents based on what I've done, read, and heard enough times to believe it.