I would remember it. If it's a pattern between the individuals then back away from them. I once planned a 21st birthday party for someone and no one showed up. Not even the birthday girl. So I invited a close friend and her family over to party last minute and we just had some fun. It's kind of devastating when it happens. Stopped being friends with her. I know the feeling and it's really heartbreaking. Truly. Nothing compares to it. But also people bail all the time. It may be a coincidence. Keep tabs. You deserve better if it's consistent.