I don't think we've ever gotten confirmation on the number of prototypes. There's been many rumors but no serial numbers or other decisive details. e.g. if we've had photos showing 36011, 36012, 36013, 36014 with the latter 3 all being DSI+TVC,
As I understand it, the grapevine seem fairly confident that at least three prototypes, possibly four prototypes have already flown.
I wouldn't use serials to try and determine anything -- we only had clear pics of the first prototype seeing 36011, and no serials of the other aircraft to date, and the only way we've been able to identify the second prototype from the first is in its visual changes of DSI, landing gear and exhausts.
If we accept that serials are no longer something we are entitled to, we are basically left to go with what the online pipeline says.
then what you're saying would be true, having 3 prototypes with the same config then reverting part of it on the 5th one would be strange indeed.
I somewhat disagree with this.
If they were making extensive changes to the overall airframe between multiple prototypes it would be odd, but if they are making specific well circumscribed changes which doesn't effect the rest of the aircraft then it is somewhat sensible.
We forget that things like exhausts are actually a subsystem in their own right, and iterating on subsystem specifics is not out of the ordinary for an EMD phase program.
More importantly, given the ambition of this aircraft overall, it probably makes sense to verify key subsystem alternatives, not only for the purpose of choosing the best one in a real world setting but also in gathering real world data beyond a wind tunnel.
