As I understand it mileage accumulation is separate from the testing over the routes to be operated. The former is just proving that the trains themselves are fit for acceptance by TPE. The urgent need is to get some sets available to TPE for crew training to start. You can do all the testing you want, but without fully trained up crews they aren't going anywhere. The longer it takes for this process to start, the bigger the problem becomes since in due course there will be a training requirement for 397's and 802's also. Crews can only be stretched so far before the service starts to suffer due to a shortage of available train crews, we've seen it time and time again. I doubt that another summer of cancellations and delays would go down well with TPE's long suffering passengers. As usual when things aren't going well, TPE have gone into 'radio silence' mode.
How have TPE gone into radio silence mode, if you don't mind me asking? Unless you mean internally and you work for TPE?
Before Xmas, they said it was delayed until spring - presumably May TT change and have been posting stuff on social about it being introduced later in the year - not sure how that's radio silence.
Even if it is again delayed as it's not ready for passenger service, isn't it more an issue about CAF too? Caledonidan Sleeper nearly 2 years late, TPE 9 months late and Northern due in May...