I think as long as you’re using any good iron remover to ensure that above surface contamination does not exist, then you’re helping the new application. So whatever you’re using, I would say keep it.
If you did it recently and you don’t think there will be any signs of color change due to negligible contaminants, I guess you could skip? But I’ll also defer to coating experts for their insight.
I'm going to use it but i have never seen the color change. I don't live anywhere near any industrial areas. Thanks!