Gerald, I believe you are a little confused as to what maintenance is and covers. What you're really referring to in your above post is upgrades, whereby you may skip a couple of years then upgrade to the latest version with a one lump sum cost for that upgrade version.
Maintenance is a yearly contract cost, which includes all upgrades, support etc , you only do one or the other not both.

If the answers to your questions are not included in Carveco's website, then i would recommend you email them direct so as to avoid speculative answers.
Gary