Yes, accessing your liscence would mean theyd really have to have full control of your computer and the ability to actually deactivate it or somehow find your code which isnt something id consider possible in any scenario (and its far too easy to pirate vocaloids these days so value wise? no real reason to do it lol).
as far as i can understand the only way to know how many activations have been used (aside from keeping track yourself) when you go to activate the vocaloid, it will often (i think) tell you again "youve have _ many activations". you can be on any PC activating a vocaloid again and will find this out, i think. i honestly cant recall if it tells you. however when i contacted a few companies, they actually knew (as its an online thing), though i wouldnt say its worth bothering them if youd like to know lol. you have 3 total i think for all vocaloids regardless.