I will discuss the need for completeness masks for the 3Pi stacked data catalogues to enable large scale structure and other related science. I will report on a pilot study performed by Danny Farrow and will highlight the issues that have to be overcome to roll out a similar data product to the full 3pi. I will briefly introduce the primary resolution elements of the 3Pi tessellation and explain that it preferable to have these form part of the geometry of the mask.