Regarding the planning applications, (unless my searching has failed completely), I‘m fairly sure that the Network Raill application for the new platforms and new overbridge is not yet online.
On the west side the main application is
21/00691/DC - it is all council work external to the station, basically to demolish certain buildings, pedestrianise the approaches, and remove car parking from the entrance building. There is a very minor listed building consent
21/00750/DCLB required by Network Rail to put a new entrance through a low brick wall into the existing off street car park, just south of the entrance building.
On the east side the main planning application
21/00688/DC - again it is basically a council sponsored application to do street works, property demolition, build a transport interchange and a multi story car park. This is a much larger package of info, but although it shows the probable location of the platforms, and a probable overbridge position, it is definitely not covering those areas in detail.
Note.
I haven’t provided links to the planning applications because such links almost always time out.
The website is here if anyone wants to look up the details:
Your portal to view current and old planning applications in Darlington
www.darlington.gov.uk