An old topcoat may or may not react to new topcoat; it is still iffy. (an old topcoat may hold where a new coat of the same paint may fail because it is fully set. (dry to the touch is NOT set paint. It may not stop drying fully for a year)
It depends on what you spray on it. Primer usually seals and separates a topcoat from the base surface. They tend to be less reactive to other paints too.
You will see any paint edges , any remaining color must have feathered edges. If it is a tint/stain/light grainy color you should be ok. (but watch for color pigment rising to the top of fresh paint (magnifying glass)