If an employer offers a bonus buyout during negotiations, that's a straight-up offer of more compensation, in the form of a signing bonus. It's hard to come up with scenarios where an employer would offer you a certain total compensation, and then revoke that offer because a different, previous company paid you a bonus. Would you expect your employer to reduce your compensation if you refinanced your mortgage, in the name of fairness, since that portion of your salary was "intended" to cover housing costs? Compensation is about estimation of value (expected to be) delivered vs costs (expected to be) incurred, in the presence of highly asymmetric information. Previous bonuses might give nice framing for certain points during the negotiation, but that's just storytelling; the real negotiation doesn't care about them, and only slightly cares about start date in most circumstances.