Thanks for the explanation GreenKnight121, what you say makes sense assuming of course that the engines in these test vehicles have not been swapped out for whatever appropriate reasons.
Keeping slightly on the engines theme, there seems to have been some silence recently about new aircraft leaving Fort Worth, am I correct in thinking that with the Titanium sourcing problems and new design being worked on that no new engines are being shipped to the Fort Worth Assembly lines? A simple answer would suffice.