Ann, in zone 6, Pittsburgh area anytime from April 15th to May 15th would be optimal for planting lily bulbs during the spring. In the Fall, the entire month of October. So, your planting time above was just fine.
By the way, the bulbs on the shelves now are not the same as the ones you purchased months ago. The lily bulbs sold in the spring for spring planting were only recently pulled from the growers coolers which gave them the required winter chill to get them ready for spring planting. They would be 'fresh' stock.
