For a tender that started nearly 2 years ago, had an announced shortlist of 5 bidders 11 months ago. By now not really being any more precise than announcing sometime in 1.5 to 7.5 months is exceedingly vague.
Introduction nearer 6-7 years after starting the process is worryingly slow unless get something exceptional at end of process, rather than average or adequate.
Anyway good to know it's progressing, even if at snail pace.
The first procurement notice was three years ago. Announcing a precise timeline when the business case requires external approval would be unwise, forcing a decision on a particular timeline is a good way to make a no more likely. Approval processes can also have unknown length, requests for further information before a decision can be made etc.
The shortlist of bidders was 18 months ago, this was also when the full tender information was sent out. I'd guess that compiling, producing and reviewing the requirements or external considerations factored into the timing of that rather than the shortlisting process itself. Most of the lessons learnt from previous fleet introductions across the industry boil down to "having X specified or factored into the contract would have made the introduction better". There are parts around managing when the contract needs altering or working around, but it's a lot easier if the contract doesn't need changing in the first place.
The business case would also need to consider how the fleet would be introduced. Are any depot works required? Are station/infrastructure changes needed? How are staff going to be trained? Do storage facilities need to be hired? How is the cross over of new and old fleet going to be managed at each point during introduction? The costs of all those plans need to be included so have to be known in detail.
I'd expect there's many people at Southeastern who could talk at length about the procurement progress and the amount of work gone into getting a good outcome. But disclosures about the procurement can open up the award to challenges and a 10 figure contract is well worth fighting over if there's any opportunity to do so. That means information in the public domain is going to be sparse and be stuff that all bidders have already been told.