Yeah, they kinda did. I could join the Legion just from being in during Lebanon and Grenada and someone who repaired mess kits at Dugway Proving Ground could join if they served after a certain date in 1990 to now. Go look.
American Legion requirements are different. You just need to serve during a time of war. I qualified to join the Legion because I enlisted during Vietnam, even though I never served in country. The VFW is different. Those that went to Vietnam were eligible, but those that didn't, like myself, were not eligible to join. I became eligible for VFW membership once I actually went to an active war zone where we never left the base except on a mission, where the enemy fired rockets at our base, where our aircraft came back with bullet holes in them and where we stood in way too many fallen comrade salutes.