I discussed with the guy from AN. 4200 indexes are made using 2MASS J-band, at 1.25 µm, completely out of the sensitivity range of our sensors. In opposite, 4100 indexes are using Tycho-2 catalog with magnitude in the visible light range. As AN algorithm is sensitive magnitude ordering of stars, it is doing a better job with 4100 indexes when using camera operating in the visible light range.
Therefore, I would suggest that ansvr download 4100 indexes when available, i.e. from 4119 down to 4107.
My 2 cents