The sales figure on which the royalty is based may be subject to some manipulation pertaining to timing (which could affect the royalty tier in a given period), inventory stocking, rebates, returns, etc.
I don't think any of this is worth worrying about, but you brought it up wrt the opt-in option on profit sharing.
Of greater consequence than the above (IMO) is the not-yet-agreed-upon percentage of value to be ascribed to the protease inhibitor relative to the overall regimen, which directly affects ENTA's royalties for both the 3-DAA and 2-DAA (if no opt-in) regimens.
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