I have weekly 1-on-1 private sessions with my students. Each student has his/her own scheduled, regular time-slot (so, 'Student A' comes on Wednesdays 11:15, and 'Student B' comes @11:50, etc.).

Now there is an event coming up that several students will be attending. Therefore I have created a Survey in order to find out who will come to their session this week and who will skip (due to the event), so I can adjust and condense my schedule accordingly. It is a simple, one question Survey with a Yes or No answer: 

Unfortunately, when test running the Survey, I noticed that some of the responses (I tried multiple mock-contacts) where anonymous, rendering the Survey totally useless. After all, I need to know  who is coming or not, obviously. Admittedly it did show the IP address of the sender, but to me this is useless information. 

Sure, I could include a field in which they could fill in their name, but I want to impose as little as possible on the students, requiring as little effort as possible.

I noticed when looking at the results in Survey it mentioned "Respondent Variables" (when it showed sender email-address):

And when these words were missing there was no sender email address:

Is there way to adjust this, so I know which response belongs to whom?

Thank you very much in advance for your feedback!!

N.B: I have integrated z-CRM