Methods and apparatus to adjust media impressions based on media impression notification loss rates in network communications are disclosed. An example method includes determining a first network media impression adjustment factor based on a quantity of lost test media impression notifications for a first network in a geographic region; determining an adjusted quantity of first network user-accessed media impression notifications for the first network by applying the first network media impression adjustment factor to a quantity of successfully received user-accessed media impression notifications to generate a product and weighting the product based on a market share of first subscribers corresponding to the first network in the geographic region; and storing the weighted adjusted quantity of the user-accessed media impression notifications in association with a media identifier to credit corresponding media with a quantity of media accesses corresponding to the weighted adjusted quantity of the user-accessed media impression notifications.