This distinction is not really an issue for me. People collected this set for many years without being concerned about it. The distinction didn't really become mainstream until well into the 2000's. Many sets from the mid-to-late '60s had card backs that were either lighter or darker. Although I prefer the goldenrod backs, pastel yellow backs are fine with me too. Actually, not all lighter-yellow card backs are Milton Bradleys, since they were only represented in the early series. There were higher-series cards with backs that looked like Milton Bradleys, but were actually Topps.