Every founder who sells a little stock in a secondary hears the same first question from their board: what discount to the last round are we accepting? It is a natural anchor, and it is mostly the wrong one. A preferred price set two years ago reflected a different market, a different revenue line and a different set of rights attached to the shares.
Common stock in a secondary carries none of the liquidation preference that made the preferred price possible. Buyers know this, and their models start from the company's expected outcomes, not from the last headline valuation. The useful conversation is about what the buyer believes the distribution of exits looks like, and how much of it the common holder actually participates in.
The terms that move real value are usually elsewhere: the company's right of first refusal, whether the transfer resets anything in the 409A, what information the buyer receives and whether the sale creates a reference price the next priced round will have to live with. Founders who negotiate those carefully tend to care much less about the discount.