Clarify when Additional Processing starts - thanks

[dude12]

When does Additional Processing actually start, is it the day of the interview when i was given 211g form?

If so does London embassy make full copies of all pages of passport on the day of the interview?

The reason why i am asking, is right before the interview date i travelled to another country, so the initial paper work (I-130) does not have new stamps of the country i visited before the interview date

thanks