In his case, according to him he yad used 2C-B very heavily many years previously, and it seems he developed an extremely high level of tolerance which remained unchanged for many years of non-use.
In the cases discussed in the thread, it's possible that something similar was happening. Indeed, many antidepressants also alter serotonin receptor expression over time, and it's plausible that in some people, these effects could linger for a long time.