A: If that envelop is opened, one sheet of letter paper and 2 sheets of 10 thousand yen bills 出てきた.
In my understanding, ～てきた represents
action done in the past and it continues up to the present, "~started to, ~has begun to, etc". For example,
雨が降ってきた。It started to rain.
人口が増えてきた。The population has begun to grow.
after doing the ～て action, the speaker return to the place where she/he says the sentence.
親を連れてきた。I brought my parents here.
弁当を買ってきた。 I bought a meal and came here with that meal.
But in the sentence A, I think the usage of ～出てきた does not make sense so ～出た should be used instead.
What is the meaning of ～てきた in the sentence A?