I think for the sorting issue you need a dual() for your calculated dimension which returned within the string-part your dimension and within the numeric-part your sort-order. I mean something like this:
Your NULL within the dimension need to be replaced to be clickable. There are various approaches to replace this, one is this: Filling Default Values Using Mapping | Qlikview Cookbook
DUAL() is a good suggestion. I will try that. And I'll have a look at your link.
Right now I'm trying to add some more possible reasons to my dimension though they may appear somewhat strange - it is still a start for analyzing the differences - but I guess there will still be a remainder.
Thanks a lot!
P.S.: That article is a bit hard to read because some software is missing on my laptop, the pics are not displayed. I can guess what they show, though. This method does look cool, but not really simpler than putting an IF_construct (using LEN() or anything to find out empty spaces) into the LOAD itself.
I think, however, I have solved the issue. I can just insert into that calculated dimension all possible data_constellations and make sure there can be no records not matchin any of them - that way there cannot be a remainder.