A "valid proxy" refers to a person or thing that can act on behalf of someone or something else in a fair and acceptable way. It is a reliable substitute that represents the original or desired entity accurately. Full definition
For the moment, I don't see tree rings as valid proxies — for temperature OR precipitation. (climateaudit.org)
You are invited to attend the Annual Meeting if you were a Google stockholder as of the close of business on April 6, 2015, the Record Date for the Annual Meeting, or hold a valid proxy for the Annual Meeting. (sec.gov)
You are entitled to attend and participate in the Annual Meeting only if you were a stockholder as of the close of business on April 18, 2018 or if you hold a valid proxy for the Annual Meeting. (sec.gov)