Data coding audit

An audit of all existing data codings to make sure that we have not missed any obvious NA value replacement or recoding rules. This MR contains the updates proposed in this google spreadsheet:

https://docs.google.com/spreadsheets/d/1ax7EaYxBK9KvwbPbFUBssUR1rmKrRcc15btieT9IR3w/edit?usp=sharing