You're quite right. I should not have said 'Torque specs are always for a clean dry thread', but rather 'Torque specs are normally for a clean dry thread unless noted otherwise'.

For those willing to tolerate a lengthy dissertation here, I did some additional reading, trying to rely on more authoritative sources rather than opinions. For a given torque, an oiled thread will normally result in significantly more clamping force than a dry thread, i.e. overtightened. A crude rule of thumb is to use 20% less torque for an oiled thread. The industry standard is for specifications to be based on a clean dry thread unless noted otherwise. Various tightening procedures involving one or more steps of torque and angle tightening can be used to achieve a desired accuracy or uniformity of tightness. It's up to each manufacturer to determine which type of tightening procedure is best for a particular grade of fastener and application. In the absence of any guideline or specification, fastener manufacturers do have published tables of default recommended torques for their various sizes, grades and types of fasteners; some include maximum torque values (above which a fastener may start to deform and weaken, known as the yield point). If a fastener is taken anywhere near the yield point it is considered single use. Even if the torque spec isn’t close to the yield point, if there's a reasonable chance the fastener was overtightened or came close to the yield point during use (such as heat expansion) then it should also be considered single use.

Cylinder heads are of course one of those mildly critical applications where you want to achieve a maximum safe clamping force (thus close to the yield point) and as well uniformity among a number of bolts. A new bolt of the proper grade and consistent quality is of course the starting point when determining specifications. A clean, oiled bolt (both thread and under the head) apparently results in more uniform clamping than a dry thread (variable surface friction may increasingly come into play as the bolt tightens). Angle tightening is apparently even more accurate and consistent for achieving a desired clamping force (such as needing to stay below the yield point or achieving a desired amount of compression). The problem with angle tightening is the starting point, which is why angle tightening is preceded by an initial torque well below the desired final torque. Additional pre-tightening steps may be used, in part to squeeze out any excess oil to achieve more uniform lubrication, but more importantly to pre-compress the head gasket and as well to pre-stress the head for improved evenness of mating (microscopically, head surfaces will never perfectly mate). A cross pattern working from the middle out is used to improve uniformity and as well to avoid deforming the gasket or head.

The Volvo cylinder head bolt tightening specifications for our old bricks were determined using a clean, oiled (new) bolt, so that's what we need to follow. Four cylinders like the B230F use a 3-step procedure. Six cylinders like the B280F with a larger head use a 5-step procedure.

Going back to our original hub nut discussion. The closer a fastener is taken to the yield point, the more accurate the torque procedure needs to be. From the above discussion, an oiled thread, multi-step, angle-tightening procedure would seemingly be the most accurate. In the case of the hub nut, the specification for an angle torque procedure suggests there's a desire for a fairly accurate tightening. Part of that may be the need to match the optimal amount of compression the bearing is designed for (as mentioned in an SKF bearing article I saw). If it's not overly critical and is reasonably below the yield point then a dry thread method may be quite adequate. Making it a dry thread spec is also better in that mechanics are perhaps not as likely to notice a footnote for an oiled thread and could easily use the normal dry method, which undertightens. It’s for those kinds of reasons Volvo felt it safe to go with a dry specification. Because that's not the most accurate method, engineers may have concerns that a fastener could inadvertently be taken too close to the yield point (say someone incorrectly uses an oiled thread) and thus Volvo requires a new nut each time just to be safe. Now if all that's true and if I was certain the factory and every mechanic preceding me didn't overtighten then it's probably not all that bad for a hobbyist to re-use a hub nut, but of course we don't have that certainty.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now