There are three certification levels on grass seed and most people have only ever seen the weakest one. The white tag on every bag is federal law, a statement of contents rather than a standard of quality. A blue tag means a land grant university pulled a sample, verified the cultivar, and held it to thresholds for noxious weed, other crop and weed seed. Gold tag, Sod Quality Certified, is what I buy. Roughly six times the sample size, zero tolerance on noxious weeds, field inspections through the growing season, and third party inspection at every point the seed is moved. It is genuinely hard to source, and I call 70 to 80 growers a year to build a blend out of it.
What is in my bag right now is three turf type tall fescues, Traverse 2 SRP, 4th Millennium SRP and Triad, plus Barvette HGT Kentucky bluegrass. All three fescues sit on UT Extension's list of statistically top-performing tall fescues for Tennessee (NTEP trials), and I picked them for brown patch resistance, wear recovery and the short rhizomes that let them repair themselves a little. Barvette HGT is the one I would point at. It establishes unusually fast for a bluegrass, its rhizomes are what knit the whole stand together, and it came out of Barenbrug's Healthy Grass Technology program, which stress tests for exactly the transition zone persistence a Giles County summer demands.
Now the other side of the shelf. Kentucky 31 is the cheapest fescue sold and the price traces straight back to the standard of care in the production field, where whatever the grower could not control gets harvested along with the crop. Dallisgrass (Paspalum dilatatum) is the contaminant that costs people the most, because Oregon seed testing classifies it as other crop seed rather than a weed, so it carries a higher allowable threshold. You plant it in October, see nothing all winter, and meet it the following July as a coarse straight bladed clump that takes me three to five years to clear out. Johnson grass and quackgrass ride in the same way. Straw used as a cover is worse than any of them.