IMHO, the minimum expected from a man page is to be complete. For example, this link does not give enough information to understand why "tar cfz x.tgz x" works, but not "tar -tfz x.tgz"
It says in the man page explicitly that it's not complete and you should look at `info tar` for the full man page. Also, because the problem really has nothing to do with tar -- every man page doesn't need to explain how old/short/long options work.
Section 3.3.3 "Old Option Styles" covers exactly the situation you describe.
> This old way of writing 'tar' options can surprise even experienced users. For example, the two commands:
> tar cfz archive.tar.gz file
> tar -cfz archive.tar.gz file
> are quite different. The first example uses 'archive.tar.gz' as the value for option 'f' and recognizes the option 'z'. The second example, however, uses 'z' as the value for option 'f' -- probably not what was intended.
> Old options are kept for compatibility with old versions of 'tar'.
> This second example could be corrected in many ways, among which the following are equivalent:
