From what I can make out on their support site - it suggests that some of the differences may be regional.
V3 appears to have additional lightning protection and better antennas. I do not aim to go through all the spec docs.
However......................
you mentioned that it supports g.inp and g.vector but in w9970 v1 datasheet it doesn't show support for g.inp and g.vector
https://static.tp-link.com/res/down/doc/TD-W9970_V1_Datasheet.pdf
can you please tell me how did you know that it supports these features?
I tested the TD-W9970v1 according to the WebGUI - see image
here. At the time (in 2016) I wasn't aware that there would be further versions
When I wrote the
review for the TD-W9770 I got the modem and specifications directly from TP-Link UK. I don't have a photo of the side of the box & I no longer have this modem, but iirc it also specified as G.993.5 & G.998.4 on the side of the box that it came in.
I am not aware of this particular model having been physically tested with G.Vector as we don't have many cabs in the UK with vectoring, but it certainly does work with G.INP.