The Association of National Advertisers has published guidance cautioning brands against over-committing retail media budgets in the absence of standardised measurement frameworks. The core finding is straightforward: Amazon Advertising, Walmart Connect, Kroger Precision Marketing, and the other major retail media networks each define their performance metrics differently — attribution windows, impression counting methodology, conversion definitions, and incrementality measurement approaches are sufficiently inconsistent that allocating budgets across multiple networks based on reported returns is, at present, an exercise in comparing non-equivalent figures. The ANA's call for standardisation mirrors the trajectory of programmatic advertising a decade ago, where the absence of common metrics persisted for several years before industry and advertiser pressure forced convergence. Brands allocating material retail media budgets without cross-network comparability should treat network-reported performance as directional rather than benchmarkable.