I think that they took all 17 of Sally’s DVDs in there with them, and that all the encoded DVDs could act as a trigger to the Tardis. After all, if there was only one in existence then it would be highly improbable that it would end up in Sally’s hands when she finally got into the Tardis. In fact, you could power a spaceship with that level of improbability.Hate to nit pick
But they didn't eject the DVD from the Laptop
and then had it again in the Tardis.
Mind, your comment does throw up another question – why did they risk life and limb going back into that house to watch the DVDs, surely it would be safer and easier just to view them at home?