Thought I'd add, I successfully followed the manual DB update instructions and was able to continue with my 2.4.0 campaign, with ATG now loading properly when I start from an existing missile with ATG, so I'm assuming ATG is now working in general.
Btw, I think you do need to set the default value of ATG under FTC_MissileType to be 1. I originally interpreted that statement by Steve as an explanation of how it worked when setting individual missile ATGs in the DB, but then read it again and did set it to 1, and it seems to be working.