I'll stake nothing on my answer...maybe this will lead nowhere, but hey sue me. I think your assumption that there IS a definitive answer to your question is false, as if there were a book somewhere containing all the rules for correct construction notation. In fact no such book exists (as far as I know). Rather construction notes are basically just generally accepted conventions between builders and architects that have developed rather unevenly over time. THus different architects do different things. For example I have never written U.O.N on any drawing, but I have written U.N.O (unless noted otherwise). My thinking, though, is that you are basically correct. Marking a condition as typical means just that. X is typical and if some conditions differ from this norm, I'd want to see those called out individually, thus U.O.N. is redundant. Of course builders and architects are not always the most literate bunch and don't always consider the meaning of words, especially when they appear as abbreviations. I think a lot of architects get paranoid about things being missed in drawings, which is not a totally unjustified fear. Unfortunately this leads to people writing things like "typical unless otherwise noted," which means nothing more than saying "this is typical unless I say this isn't typical."

yes, but doesn't noting something as typical do the same thing? In other words shouldn't the "unless noted otherwise" be implicit? If I say something is TYP. and fail to call out the areas that differ, I'm in exactly the same position that I'd be in if I'd said TYP. U.N.O and failed to note otherwise. I understand being careful, but still seems redundant to me.

"typical unless otherwise noted" is used constantly in specifications, and not always just written by architects (I see this all the time in lighting and electrical specs in particular.) It does just mean "this is always the case unless you see that it says something else in reference to a particular incidence".
The reasons are exactly as you stated. One phrase could be construed to negate the other, if used alone separately in the same set.


"unless otherwise noted typical" is not the usual order of the words, but I don't see the meaning changing there...

agree w/oldfog, TYP. means the condition is the same everywhere, the U.N.O. designation red flags it to mean there ARE discrepencies elsewhere, not that there 'might' be changed conditions.
Some people always put the U.N.O. designation in just to cover their arse in case they change a detail and it isn't co-ordinated elsewher in the drawings.

you don't have to include it. but you might want to in some instances, as those described above. that's the answer.

usually this kind of language is used because someone some time in the past got stung. my specification language and the notes that i, personally, add to drawings are fairly specific to me because they represent the 'gotchas' of past projects.

i am speaking for small projects, like houses;
sometimes i say on the drawing, pointing out to a condition (typ.) except in -say the location here, and point out where the exceptional detail is shown etc.-.
a good thing to remember when drawing the project, is to put yourself in builder's place and be as clear as possible walking them through your project.
anything in regards to, size,quantity and quality is very important to the builder.

ps;
i wouldn't 'stake' my license for even a typical sheet number location in this business.;)