I'm pretty sure it's already covered in the War Room, in the post zgrssd wrote about model design. There's also a DasTactic video on the topic.
To get to the point, model III does only benefit from the field testing of model II, and not from model I's. As far as I recall, you don't even have the option to improve upon model I anymore once model II is designed, only to build upon the latter. So basically, further field testing of model I is wasted as soon as you have designed model II. But model III will benefit from the increase in Base Design model II got from model I's field testing when it was designed.
Wait a minute, in the linked post, zgrssd writes
Wich means the Mark 4 may be based on the Mark 2 again.
That contradicts what I was thinking.
Admittedly it's been a while since I've played. If one can select a model older than the latest as the base, then that changes a lot.
Honestly, I've always upgraded troops as soon as models were developed because I had the resources and the Base Design improved, and thus the stats. So that maybe is why I had never really looked into building a model upon version N-1.
< Message edited by Jdane -- 8/7/2020 1:02:21 AM >