It seems like it would be more work anyhow. When you use a stencil to repaint, you paint over a clean basecoat. If you were to retrace originals, you'd have to maintain clean lines on both the stencil and the basecoat unless you're leaving the base color as is. But, with clean paint as your stencil colors it won't look right having the original base on there. It would almost certainly be yellowed or dull.