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I'll use the same basic structure for generating TAFTOs as I did for generating Nows, consisting of both advertising (what Drew is doing) and WOM. As with Nows, I'll presume some fraction of TAFTOs lose their zeal each year; I'll presume that they return to being normal Nows.

The only real difference between a Now and a TAFTO is their infectiousness. I'll presume that interactions between a NotYet and a TAFTO are more likely to lead to a new Now than interactions between a NotYet and a Now. You can see the full model if you want; I won't go through it here.