It is something that was negotiated between the agent and nb. Common practice would be to include it in an offer sheet if it was negotiated.
Presumably any contract nb produced would have elements, such as a morals clause, that aren't listed on an offer sheet. That is why material elements that are central to negotiation get included, so nobody wastes time drafting a contract that has elements which have been discussed and not agreed to.
In other words, if Berian's agent had been assured by nb that reduction clauses would not be in any final contract, it is in his client's interest to have that on the offer sheet.