As you surely understand - this is a mine field you're stepping into with this question. But it's great fun and I'll do a reasonable try to answer this question. So lets start in the beginning, shall we?!
Software versioning is the process of assigning either unique version names or unique version numbers to unique states of computer software. Within a given version number category (major, minor), these numbers are generally assigned in increasing order and correspond to new developments in the software. At a fine-grained level, revision control is often used for keeping track of incrementally different versions of electronic information, whether or not this information is actually computer software. Reference: Software Versioning
That said there is no convention of how many groups of number to use. Some use four groups (like Microsoft), others three. The important thing to remember is that the order is left to right. 1.0.0 is greater than 0.9.9.
There are some developers who use 0 for alpha version, 1 for beta version, 2 for release candidate and 3 for final and production ready.
Some rare cases like SmartEiffel use negative numbers starting at -1.0. The S.u.S.E Linux distribution started at version 4.2 referenceing 42, "the answer to life, the universe and everything" mentioned in Douglas Adams' The Hitchhiker's Guide To The Galaxy. The current Slackware version is at 13.37 referencing leet.
So it's fair to say that anything you use is neither right nor wrong. The advice would be to use a versioning system that works for you, and that you document how your versioning system should be read.