Is there something I am missing here?
After manufacturing tension tends to drop over time so starting off with a '+' may not be entirely bad assuming it isn't extreme and that it doesn't cause the materials to deform more than permitted. The way I understand it: you apply a certain torque to a fastener in order to get to minimum levels of tension and friction (which still have an engineering reserve) on the fastener itself to guarantee a seal and to stop the fastener from coming loose, so under-tension is far worse than over-tension as long as the over-tension does not result in damage to fastener or the materials, and the allowed tolerances for over-tension are quite large (up to +150% or so normally before any permanent deformation would occur).
Unless you are using 'stretch' bolts which tend to elongate to accommodate any over-tension to end up with something quite close to the intended value. This stretching tends to be non-elastic so you'd have to replace a stretch bolt every time you unfasten it or there is a pretty good chance that it will break and/or that the threads under the ending position of the nut will have deformed so that they end up being stripped if you refasten them because the nut will travel a bit further on every refastening.