The Jupiter lenses were based on Zeiss originals and, as such, the focussing helicals are for Contax, and not Leica. I don't know the numbers, but it seems that the helicals have a slightly different pitch. When the Zeiss lenses were converted to a Leica fit, they retained the Contax helical pitch, and the cameras were then designed to give correlation between RF patch and actual focus at the film plane.
If you take a Jupiter lens and put it on a Leica, there may well be a point where there is correlation between RF patch and actual focus, but it will drift out at other focus distances. How much of an issue this is depends on the depth of focus in a given circumstance. The 35mm Jupiter-12 (Zeiss Biogon) stopped down and focussed on a fairly distant object wouldn't be much of a problem, but a 50mm F1.5 Jupiter-3 (Sonnar) wide open and focussed close could well be out.
The fix is to partially dismantle the lens and adjust the position of the optical assembly within the helical mechanism. In other words, you calibrate it for best accuracy at short focus distances, and let increasing depth of focus with distance take care of the rest. Basically, you tweak the lens and focus on a target with the RF patch, and then check focus with a ground glass on the image plane (using a loupe). When they coincide at close focus, put the lens back together.
The calibration itself isn't too difficult, but you have to be confident with not losing tiny screws, which means having suitable tools and a steady hand. There's a fair chance that the grease in the helical (and diaphragm) will be dried up and need replacing, so you'd be half-way there if you were doing that anyway. Or, if you were to send the lens off for a CLA, send it to somebody that can calibrate it for Leica.
Last I looked, which was a few years ago, the f1.5 Jupiter-3 was starting to get pricey (£100 or so), while the f2 Jupiter-8 (also Sonnar) was still fairly cheap (£30-ish). A J-3 plus CLA is probably going to cost enough that looking at other options is viable. An early style J-8 might be worthwhile depending on what the CLA costs. (Later style J-8s aren't as nice - lots of the lens, including the aperture scale, rotates when focussing as a result of the mechanical design changing to make them cheaper to manufacture.)