What does it mean when NDI = 1 and RV could be 0, 2, 3 or 1?

Specs & Protocol Testing
2

NDI 1 alone doesn’t represent new data.
It’s only when the NDI bit is toggled for a HARQ ID, the transmission along with that toggled NDI represents new data

RV is basically redundancy versions.
Each RV contains different parity bits which help with increasing the probability of successful decoding.