The "Science is done by Quantity" achievement has a description that says you need to extract a mission with at least 15 common samples. I've done this with my friend multiple times now, but the achievement has not been awarded.
I've read online that you have to be playing solo for this achievement, and that you as an individual player need to be holding at all 15 (or more) samples (i.e. it cannot be spread across teammates). But I've read some conflicting information on these statements.
Furthermore, there is an additional, similar achievement called "Science is done by Quality" in which you must extract with at least 15 rare samples. I've read online for this achievement that the samples can be spread across teammates. While I guess it's possible the two achievements work differently, I would find it strange if they did seeing that the only difference in their descriptions is the type of sample to collect.
What are the requirements to unlock the "Science is done by Quantity" achievement?