Sorry for the delay in my reply, but I work part-time.
As to your question about the spotty emergence of the new grass, the problem maybe the "on and off" rains. Grass seedings need to be kept evenly moist for about a week to insure uniform emergence. A new seeding of grass can require some babysitting that first week or so, if it does not rain frequently and keep the soil moist. Otherwise, you need to water (irrigate) the seeding everyday till the soil surface "glistens".
You might want to check this publication from Oregon State University: http://extension.oregonstate.edu/catalog/pdf/EC/EC1550.pdf
Another issue would be just the opposite of the above scenario - too much rain too quickly and the grass seed is washed to the lower areas. This would cause a spotty appearance as well.
Those are the two most likely scenarios for your spotty emergence problem. I hope this is helpful to you-