Loop 1 is filling your D/T grid (and other grids, such as hidden date and hidden month) with one cache per cell. Loop two is to fill the grid with 2 caches per D/T, and so on.
So when the D/T grid is reporting cells missing in the next loop, it is allowing to you future plan so that while working on this loop you can work on the next one as well.
If you are a paying member of PGC then when you set the D/T filters (your profile name and country) there is also an "Add filter" field where you can specify the loop to examine.