12,002
In words? Two thousand twelve. But if you mean numbers, then it's 2,012
502,012
240,012
5,212.51
The correct way to write the year on an invitation is "two thousand twelve." This follows the standard format for writing out the year in words.
2,012
Two thousand twelve.
The number makes no sense since twelve hundred is one thousand two hundred, and twelve thousand is one ten thousand and 2 thousands. You can't have 2 numbers occupying the same space in a number which 1 and 2 do in the thousand digit. However, one could propose that you add the two together giving 13,212
two thousand twelve
Two thousand twelve.
Two hundred twelve thousand, five hundred.
This is how you write six billion two hundred million twelve thousand six: 6,200,012,006