Tax
Closing agreements sound in contract, and therefore do not bar subsequent assessments to the contrary, as the tax authority is a direct exercise of statutory authority. The disparity provides a basis for challenge according to the usual means.
All members of a partnership are not parties to a settlement agreement with the Tax Partner of a partnership, so the relevant statute of limitations runs from the entry of stipulated judgment.
https://d3bsvxk93brmko.cloudfront.net/datastore/opinions/2016/01/25/13-16458.pdf
Since 2011. An occasional commonplacing of the U.S. Circuit Courts of Appeal.
Neither an authoritative statement of the law nor legal advice. Quick work.