Thanks for these. I have 197006 delivered on 24/11/21 - being the date is was first reported as being at Castle Donnington (per post #1,555 of this thread). Although this may be erroneous as whilst it had been delivered from the factory, it hadn't been delivered to TfW (it seems I'm not always consistent either!).
It seems to me that the definition of 'date delivered' isn't consistent across threads in this forum and other railway sites and publications - similar to what constitues a train being withdrawn (off-lease / stored (un)/serviceable, etc). I get the impression that for 'date delivered' most use date delivered to TOC/FOC - but sometimes it seems date delivered from the factory or date delivered into storage or some other criteria is used - with variations covering mileage accumulation / shakedown running, etc. And then there's date accepted by the TOC, date the TOC starts paying the lease for the unit as well - although these are probably more related to 'date into service' - which is also blurred - with some sites, not all, using first day in public service, and others using dates relating to legal / financial status.
Looking at the content of this site, and others, I reckon the criterion that's generally used for 'date delivered' that's used is date delivered to TOC, although date delivered into storage seems to be used quite a bit, and other criteria as well.
I'd be very interested to know what criteria you use for determining 'date delivered' - and also from anyone else - it would be good if there was some consensus as to how this is recorded. Or perhaps there is - and I'm just over-complicating things!
Many thanks