Buttwing - you are right, the content does vary.
Many areas now use the CEM exams, which cover subjects similar to school curriculum.
You need to find out which exam is used by your area. It is interesting to read how many different exams you have. I know that in Glos and in Kent (for example) it is one exam for the whole county.
11plusforum will give you all the information, but be warned people are very ahem focused on there.
Some areas still use just VR. This then requires you to buy the book and work through the 21 different types of VR questions, and use the book to learn tricks to use to help you.
You are right that NVR is not taught anywhere. But you simply buy the CPG produced book and work through it. It is pretty straightforward. There are about 8 different things to look for in a NVR question, things like shading, number of sides of shapes, patterns etc.
It is often said that the exams include maths way beyond the level of year 5/6. I am a little skeptical about this. Ds is very good at maths, he got level 6 in year 6. He passed his 11+ to a super selective grammar. He was put into the top set, and they then covered lots of the things he had done for level 6.
I know that our area is not nearly as competitive as some, but the school was not expecting the kids to be at year 8 level at all as they came into year 7.
Dd1 has just passed her 11+. (CEM test) She passed well enough that she is guaranteed a place at the super selective. We covered all the material in the CPG books. I made her know it well. It was all school based curriculum that she had covered in school, but she needed to know it so she could use it very quickly. She said the exam was easier than the practice book, as were the NVR questions.