What IP issues kill a deal in due diligence?

Broken ownership kills more deals than weak patents. The most common findings, in rough order of frequency: an inventor, founder or contractor who never signed an assignment, so the company does not own what it says it owns; a founder whose previous employer or university has a claim on the core invention under an employment agreement or institutional IP policy; a public disclosure, publication, demo or launch before the first filing that invalidates the key application outside the US; an open-source component under a copyleft licence such as GPL or AGPL embedded in a product the company claims as proprietary; lapsed applications or patents where a deadline or maintenance fee was missed; joint ownership with a partner or university with no agreement on who may license or enforce; and a competitor patent nobody checked that the product plainly reads on.

Most of these are fixable, and investors and acquirers distinguish between fixable and fatal. A missing assignment can usually be signed, provided the person is still reachable and cooperative, which is why it should be done at hiring rather than at exit. A prior-employer claim can sometimes be released or licensed. A missed disclosure cannot be undone in Europe, but the US grace period or narrower claims may salvage part of it. What turns a fixable issue into a lost deal is discovering it in the data room instead of disclosing it upfront with a plan. The lesson that recurs in every post-mortem: assignment language matters. Agreements that say the employee "agrees to assign" future inventions create only a promise; agreements that say "hereby assigns" transfer title automatically, the distinction at the heart of the Stanford v. Roche litigation. See also Do I need an invention assignment agreement?