I don't have a heavy layer of dead grass and my lawn is not very built up so is it necessary to get the new seeds to grow? I read that you need to dethatch only if the dead material is over 1/2". Mine is much less.
For grass seed to germinate it must be in contact with the soil, so when over seeding you need to dethatch or your germimation rate will be extremely low... much better if you aerate too. When the seed sits atop the thatch (regardless how little thatch) not only won't it germinate but the birds will eat most of your labors the very first day. Even when doing a superb job and followintg all the directions the birds will still devour a substantial amount of your seed... that's why it's called OVER seeding, as in an OVER abundance of seed, much more than would be necessary if there were no birds. Birds are attracted to grass seed like a magnet, that's why when many people put in a new seeded lawn the last thing they do is cover everything with a few inches thick blanket of straw to deter the birds.
If you have thatch, it is good to dethatch. This problem will persist if you don't water properly. That is what causes thatch to build up. It's the roots staying on top of or close to the top layer of soil where the water is. Watering deeply removes this problem. One inch of water will percolate down approximately 8 inches, so that's how to water properly...till the lawn area has had a full inch. How often you do this depends on many other factors which you didn't ask about, so I won't bore you.
If you want to use perennial rye or fescue for winter turf, and if you determine whether or not you have a thatch problem, you simply broadcast the seed or put it into a spreader, preferably not a drop spreader. After you lay down the seed, take your leaf rake and tool it around to help the seed drop to soil level. You must water daily until the seed germinates. To get better results I would say, if you have the money to call someone to core aerate the soil, broadcast compost to a depth of 1/4 inch, then broadcast grass seed and gently rake it in with the leaf rake.
The type of compost which is best for this purpose, provided you don't have trees, is bacterial compost made of cow manure or other animal manure which has been well composted. Horse manure will have a lot of weed seeds so for turf I don't recommend it unless that horse manure along with the pine shavings from the stalls has been kept hot for at least a month before turning it, then hot again for another few weeks, and turning it over and over until it is thoroughly and sufficiently decomposed, rendering seeds non-viable.
Too much information? I do tend to do that.
regards, victoria
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