What do you mean by sanding? With a machine? I am sanding it by hand and the paint do not come out. I don't understand if I need to strip it or not. Many here say to sand. Is sanding with the machine that will remove the paint? I don't think so, I did sand a lot and the paint that is still there looks very sticked but it's true that if I go with a razor blade it comes out but it's not so easy.If you can scrape it off with a razor blade it's not properly adhered to the gel coat, as Wolly says. Another coat of paint on top of this won't stick any better. Get sanding, otherwise you will be scraping the new paint off with a razor blade in a few months. A few hours now will save a lot of time and expense in the long run.
We all like a short cut but most of us have found out the hard way that it's rarely worth it. If there's one thing I've learnt from this forum it's that good preparation is everything.