The original code never stops being free, but the code incorporated into a new project will be, so it's a misleading term to people unfamiliar with open source licensing, that may think the license somehow expires. Even the fsf doesn't use such terminology. They use reciprocal and nonreciprocal, because it translates the idea that gpl-like licenses create a relationship of reciprocity, and bsd-like ones create a relationship of non reciprocity.