Grass seed labels including the one for TifBlair Centipede Grass Seed are required to include certain information, including the Lot Number, the test date, and the sell by dates. Typically this is within a year of harvest but the bag you receive will have the info on it.
Without knowing what type of turf your currently have and what turf is most successful in your region, we recommend contacting your local Master Gardener for recommentions on grass seed, herbicides and treatment procedures in your area. After speaking with the Master Gardener, we will be happy to help you choose the best product for your needs.
The TifBlair Centipede Grass Seed comes in two different sizes: a 1 lb. bag that covers 2,000-4,000 sq. ft., and a 5 lb. bag that covers 10,000-20,000 sq. ft. From your description, it sounds like one of the 1 lb. bags should be sufficient.