Many thanks mr. Grimm, you just saved my life. Well, figuratively speaking at least.
Perhaps this will help someone though:
I have a 2500 frame animation and two separate texture sequences, each only 150 frames long, one starts at 400 and finishes at 550 and the other one at 1300 and then finishes at 1450.
So obviously this was an issue as the script by default just starts at frame 0 of the animation itself + annoys with "missing rgb for frame xxxx" for the other 2350 frames.
So I just populated the rest of the frames with either the first or the last frame of the texture animation (so that I had 2500 frames total) and used batch renamer to accurately place the texture sequence with the rest of the frames where it belonged (say, the actual 150 frame texture sequence would start at frame 400, whereas previous 399 frames would be just the same texture from the sequence, the very first one - vice versa on the other end to 2500).
Hope this helps someone.
Asus V Extreme motherboard, i7-5930K CPU, 32 GB DDR4 Quad Channel RAM, 3x Nvidia Geforce 1080ti, Windows 7 Ultimate 64, 3DS Max 2019 64