How often do you measure effectiveness and revisit messaging?

Messaging is never set it and forget it. We typically work with the rest of the marketing organization to ensure we're crafting what we call the 'red thread' between top level brand and campaign messaging down to bottom of funnel product messaging. Brand campaigns can often last a year or more in order to see effectiveness so our mid to bottom level messaging is what we're updating more frequently as the market shifts and product changes. Typically we're updating 2 big refreshes of our Product Messaging Source Document that is used across different teams and smaller quarterly refreshes for new features, changes in market, or even to incorporate fresh new proof points with new customer stories.