The millions of calculations involved, had they been done by

The millions of calculations involved, had they been done by hand, ______ all practical value by the time they were finished.
A) had lost B) would lose C) would have lost D) should have lost
我知道正确答案是C，可是想知道为什么不能选D，老师给的复习资料里if表将来的虚拟语气的主句可以用would/should/might/could+have done,为什么这里would行，should就不行呢