Elementary, I know, but for goodness sake
copy/scan everything
NEVER EVER trust any jobsworth officialdom.
When they foul-up, it's very easy to "lose" your paperwork or totally deny ever having had it in the first place.
Of course, they're all scrupulously honest,diligent and supremely competent and never ever make mistakes....the previous paragraph is all a figment of my over-active imagination.