The “sectors” in the resulting level data have to be convex for the doom engine. The “asset pipeline” handles that by breaking up non-convex geometry into smaller convex sectors. So, there are no loops or holes in the actual level data, also from the cursory glance both of the large loops in Deimos Lab are actually not complete loops, but they have a place where the loop is broken. But that does not matter that much, as almost any level contains geometry that is either concave or has a hole (courtyard in E1M1, both large rooms in MAP01…)
