I seeded my side yard with a brand that claimed 'full sun shade mix' and my neighbor used a dirt cheap bag from the farm supply store. 6 weeks later his patch is thick and green while mine looks patchy and sad.
Figure it's more about the soil prep than the label. I've used both fancy and cheap seeds and the cheap stuff usually wins if you actually loosen the dirt and keep it wet. Your neighbor might have tilled or raked his patch better than you did yours. Grass seed companies put whatever they want on the bag, it's not like they test it in actual yards. Try watering deeper and less often next time, that's what worked for my patchy spots.