Alison gave me an idea - what if the (obviously quite often) missing treadlings in Swedish pattern books gave Davison the idea to "always" use tromp-as-writ?
(I leafed through Davison, and don't think she really does that "incorrectly" very often)
But: whence came the idea of tromp-as-literally-writ for jämtlandsdräll?
Now I have a theory: many (Swedish) books tell you something like: (usually after an explanation of how to determine the tie-up) "the treadling proceeds according to the profile threading" (trampningen följer partisolvningen)..
So, if you are not good at reading Swedish, this may look almost like "treadle as threaded" - with the little difference that we (Swedes) read it as, well, profile threading.
For jämtlandsdräll, determining the tie-up can be somewhat trícky. Below is my attempt to translate from Varp och inslag (ISBN 91-27-35226-9 B):
Two shafts will be tied to each pattern treadle.
If two blocks weave pattern at the same time, tie the shafts that are common to both blocks. Ie: block 1 is threaded on shafts 1,2 and 4, block 2 on shafts2, 3 and 1. Shafts 1 and 2 are common to both blocks, and are tied to one pattern treadle.
If one block weaves pattern [where the others do not], then tie two shafts that do not give pattern in other blocks. Block 1, for instance, can be tied two ways: either shafts 1 and 2, or shafts 1 and 4.
If the pattern contains both "single-pattern" and "double-pattern" blocks it is easiest to start with the "double-pattern" blocks. "
(Probably not the best of translations, but...)
After experimenting with a very typical jämtlandsdräll profile, making substitutions according to (slightly) different rules, this is what I have got:
Substituting it "our" way, we get this:
As you can see, the pattern treadling follows the profile treadling, with tabbies in between. (Of course, in this instance, the profile treadling does not follow the profile threading)
Using that same threading, but woven-as-literally-drawn-in, we get:
We will never get the correct pattern - (ie the pattern the profile shows) because the treadling order should be different.
Letting PCW do the block substitution (and then fixing the tie-up - jämtlandsdräll tie-ups should always "be determined" os of above):
But - isn't this another variant of the pattern?
Making it two repeats (and turning the picture, hoping for better visiblity in blogger's new picture-handler) shows that it is indeed so:
Letting PCW do the substitution in "twill form" gets us something very like the original profile (after fixing the tie-up, of course). The differences there are can probably be "massaged out". The reason is that this follows the original profile treadling.
(I extended the pattern repeat to two, in most figures, to get a better wiev of the overall pattern. In other pictures there is one repeat plus one block to balance.)
So, getting back to the original question - whence came the idea of tromp-as-literally-writ for jämtlandsdräll? Why are we not to follow the profile?
And, even curiouser: from where did (Tidball, I think - read it in an American book anyway) the idea of a tree-colour rotation come? (I don't remember if something was said about colour values, so I just used red-orange-yellow):
But then, on the other hand, as Atwater writes (link goes to the document on handweaving.net):
(ETA: seems I "fooled" the picture viewer: all pics become reasonably big if clicked, even the turned one!)