Alexander, Not till = the negative condition continues until the time indicated (after Christmas). ------- It was AFTER Christmas that Dick managed to establish contact with Nagarajan. = Dick established contact after Christmas. It was NOT TILL after Christmas that Dick managed to establish contact with Nagarajan. = He was not able to to establish contact IN THE TIME UP TO Christmas, but he managed to do it AFTER Christmas.

After December 25th

= not until after Christmas. He didn't establish contact until after Christmas