Any bat potentially could be made at Robertsbridge. If there is a shortage of a certain model/grade mid season, they may well produce a quick run themselves rather than wait for their factory in India to make and send them.
Typically it is custom mades, samples, prototypes and professional players bats that are guaranteed to be made in the UK.
You can identify a UK made bat if you know what you are looking for, but you can't simply say 'right i've bought ''model x'' so this means it has been made in India/The UK''
GN run their own factory in India, they don't contract out other suppliers to produce their bats like some brands. I have India and UK GN bats in my bag, both types are equally enjoyable to use.