Hello,
In theory yes, you could define as many different groups in the CSV as you’ll have participants. Two problems though are ensuring 1) that each participant is really assigned a different group than any other participant, and 2) that you really have the number of participants you expect.
Practically speaking, you can try to address the first point by incrementing the counter as soon as the experiment page opens. It would still take a few milliseconds though, so you might end up with some participants being assigned the same group if they take your experiment at the same time. This problem is really hard to avoid.
The second point is particularly problematic when using recruiting platforms like MTurk or Prolific. The problem here is that several people will start taking your experiment and quit before the end. If you’re incrementing the counter whenever someone opens your experiment, those participants will mess with group assignment.
The ideal solution would be to recruit all your participants first, assign an individual group to each of them, and then run the experiment. I don’t know if that’s an option for you. Or if you can afford it, you can run one participant at a time.
Remember that you can force a group in the URL by using this format: https://expt.pcibex.net/ibexexps/example/example/server.py?withsquare=0 (the 0 here means “run the first group”—use 1 for the second, 2 for the third, etc.)
Jeremy