When a contract is signed, then the adoption agreement (that is supposed to mirror the contract) has a conflicting statement, which takes priority?
which takes priority?
Based on the context as stated in your comment, I assume that the client is not the draftsman of the contract. In that case, the client is free to choose the statement in the contract or the one subsequently furnished to him via the adoption agreement. This outcome is akin to --or consistent with-- the doctrine of contra proferentem.
See also the Restatement (Second) of Contracts at § 215:
where there is a binding agreement, either completely or partially integrated, evidence of prior or contemporaneous agreements or negotiations is not admissible in evidence to contradict a term of the writing.
Thus, bringing up the existence of the [previously] signed contract would not help the company's attempt to invalidate the conflicting statement in the [subsequent] adoption agreement. Instead, it is likelier for the conflicting clause of the agreement to be cognizable as waiver of what was stated in the contract.
Perhaps the draftsman of the adoption agreement could prevail on grounds that the error in the adoption agreement would lead to an absurd outcome, but that requires a more detailed knowledge of the circumstances. If the adoption agreement is detrimental to the company/draftsman, the best approach is to amend it as soon as possible.
A situation where the adoption agreement is detrimental to the non-draftsman of the contract sounds in company's unilateral alteration of the contract. As such, it would be unenforceable because it cannot be said that the client agreed (or would be reasonable for him to agree) upon the new, detrimental clause which is inconsistent with what he signed.