If a survey is anonymous, there is no connection between their personal data from the token table (name, email, etc.) and the results. Thus you can't later make a connection to that in another survey.
I am not sure, but I think the tokens won't be stored in the answer tables in case of anonymous surveys. Otherwise you could make connections again, which would undermine the purpose of the survey being "anonymous".
So I think what you are trying to do, will only be possible if your survey is not anonymous.
If you need the survey to be completely anonymous, you will have to live with the disadvantages of this (not being able to recontact them, not being able to connect the survey results with the token table).
I am also not sure, but I don't think you can pass on the information about "control vs. experimental group" from the token table. Because if this would be possible, you could undermine anonymity as well.
I answer at the LimeSurvey forum in my spare time, I'm not a LimeSurvey GmbH employee.
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