Both are correct--what you are seeing is a difference in verb forms that would occur even if the sentences were taking place in the present.
The Aristotle examples describe an ongoing situation
and an accomplishment
that would both be described in the present perfect:
John has been a poor locksmith up to now.
John has traveled to many countries, and is now moving to New Zealand.
Our example is an action that would be described in the simple present:
As Laura leaves, she locks the door.
So, when you add "before," present perfect becomes past perfect:
He has been working as a children's dance instructor.
Before he was discovered by a talent scout, he had been working as a children's dance instructor.
Simple present or present continuous becomes simple past:
Jack is confused.
Before he took Dmitry's class, Jack was confused.
I am eating the rest of the cake.
Before I took went to sleep, I ate the rest of the cake.
I hope this helps!
Dmitry Farber | Manhattan GMAT Instructor | New York
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