Sharon and Peggy technically were introduced in the same issue, with Steve being morose about a WWII fling (Peggy) and then meeting a woman who looked similar (Sharon). Peggy wasn't really a major character and really only existed to fill in the backstory for Sharon, who was the main love interest until she was fridged, and later once again became a love interest (will they/won't they) until Brubaker hooked them back up. They've been going strong since. Prior to the MCU, I would argue that Peggy was more or less a footnote to the lore.