Ajlittoz, I am sore about the wiki issue. I was not aware of it and I do not know what I did to make it a wiki. Nevertheless, I will pay attention and make it right next time. Thank you for alerting me about this.
As to your proposoals, they are not what I need. The first one - that is, using left and right side style - is something I already use for other reasons. But it does not allow me to skip numbering a page; it only allows me to skip printing its number.
As to the one using field and formulae, you have come to the same conclusion I had: they are not updated after each page break. So, they do not work.
Your third alternative is unfeaseable. Copying frames page by page is not only an error prone, labour intensive task, but also quite confusing when you have tens of people applying the idea to hundreds of different documents every day. Artesanal work like this would work for once-in-a-blue-moon job, but not for regular production.
For the same reasons I can not take advantage of your last suggestions (the one using PDF). It is still more lavour intensive and much more complex.
Do you have any experience with basic macros? Perhaps I could use a macro that is called every time there is a new page break. The macro would test if it a new sheet (even or odd page number) increment an internal counter and return the result to be paste onto the header just before it is printed.
For the time being, I don’t know how to do this, but is might work.
Thank you for your help.