"We will only retain your data for as long as necessary to fulfill the purposes for which we collected it, including satisfying any legal, accounting, or reporting requirements. ... In some circumstances, we may anonymize your data (so that it can no longer be associated with you) for research or statistical purposes, in which case we may use this information indefinitely without further notice to you."
There is no specific retention period defined, and anonymized data can be kept indefinitely without notice, leaving users without clarity on when their data is actually removed.