We introduced additional validation code for TTL indexes in an earlier release cycle, as well as code to fix invalid expireAfterSeconds values for existing indexes. Additionally, we introduced similar logic to normalize any non-integer expireAfterSeconds values to integer values in SERVER-77828.

After we have gone through a major release cycle, we will know that future versions of the server will never see those invalid index specs on disk, as they would have to have first upgraded through a patched version which would fix the spec.

While we'll always need the validation code during index creation/modification, we can remove some of the extra logic associated with fixing existing indexes.