I think the best way to get two panels identical (such as cabinet sides), is to cut out one panel, smooth it and and get it "done", then lay it on top of a new piece of wood and mark it on the "new" wood, maybe just a little bigger than the done panel.
then remove done panel, cut out new piece with jigsaw or whatever, then replace done panel and clamp it to new piece. Then take router with proper bit and trim new piece to match done piece exactly.
im sure there are easier ways but i like doing things the hard way, apparently. LOL