Your example pretty much defeats your whole point. Sounds like the data isn’t complete and Boeing hasn’t shared data, which the customers want. So, the “real world performance” is not known.
That is not the way it works, Boeing already had performance data before the first aircraft was ever built, and that was shared with airlines under NDAs so they could assess the airframe before purchasing. These 10+ hour long flights, takeoff/landing tests, stall tests etc they have been doing is validating/tweaking the models, it is not creating them from scratch.
Yes Zeke - Boeing have some data from design modelling and acceptance of orders. Validating or not as the case may be; we have heard the aircraft is over-weight.
Normally during production testing we get some information from manufacturers into the media about the test and certification programme that talks positively about the aircraft, its performance and handling characteristics, etc. Key messaging. This has not been flowing with the 777x. Boeing has been quiet and on the heals of the 737 Max issues, and plenty of change within Boeing management, all we have is published notices of problems and many delays.
A well known Airline CEO is recently on record for saying that they wouldn't take delivery of the aircraft if it didn't meet it's delivery timeline or performance specs. Why do they say such things publicly with no response in Boeing's messaging over the last couple of months? We can speculate - and it's no wonder there is precisely that, speculation, given what else has been in the media, regarding the jet's certification.
The statements from Calhoun quoted above don't match the messages coming from one of their top customers. Boeing has not countered this with any statements reported here. This does not provide confidence to the public that the certification is on track or meeting or beating its promised performance specs. With Airlines making statements as mentioned, why would Boeing not do this? What's to lose? Yes, the data at this stage in any test programme is confidential - NDA. But that doesn't mean a vacuum of info, either. Boeing know how to do this. Or at least they did. Airlines may or may not be on board. What we have is ambiguity.
We know things are significantly delayed and that the FAA is taking a closer look than in recent times at the process for this. We know there are some significant issues which have emerged in the certification process for attention that have pushed out the certification date by years beyond that originally promised to launch customers. And this is a derivative rather than totally new airframe. Some Airlines will be happy to accept the delays given the current situation and the altered certification and delivery timeline. Others, less so. To be talking about relatively few deliveries (see above) in the next 10 years for a derivative aircraft which is said to be overweight and no messaging in the media on efficiency / performance to this point - doesn't engender a whole lot of confidence in the product.
Therein lies one reason why people in this forum and outside, including some at airlines, may be making the statements they are....