Breakdown of Наш контракт действовал с две тысячи восьмого до две тысячи двенадцатого года.
наш
our
два
two
год
year
тысяча
thousand
Questions & Answers about Наш контракт действовал с две тысячи восьмого до две тысячи двенадцатого года.
Why doesn't две тысячи change to the Genitive case after с and до?
In Russian, years are expressed using ordinal (ranking) numbers. When a compound ordinal number changes case, only the very last word changes its ending. So, "two thousand" stays as две тысячи, and only the last words (восьмого and двенадцатого) take the Genitive endings required by the prepositions с and до.
Why is the word года only used once at the end of the sentence?
When you state a range of years, you only need to put the word for "year" after the final number. It is understood that both numbers refer to years, so saying с две тысячи восьмого года would be grammatically fine but sounds repetitive and slightly unnatural here.
Could I use the preposition по instead of до to mean "to" or "until"?
Yes, but you would need to change the grammar. до takes the Genitive case (до две тысячи двенадцатого года) and sometimes implies the period ended right before 2012. If you use по to emphasize "up to and including" all of 2012, it requires the Accusative case: по две тысячи двенадцатый год.
Why is the imperfective verb действовал used here if the contract is already completely finished?
We use the imperfective aspect because the sentence emphasizes the duration of an ongoing state. Even though the action is over, whenever you highlight how long a continuous state lasted in the past (especially with a clear "from... to..." span), you need an imperfective verb.