At an Elo level of around 2000 they converge. (I.e. both lichess and chesscom calibrate their algorithm to match on-the-board standards around that region.)
For various reasons, online Elos are inflated by 100+ points if you go above 2500+ or below 1500. A progression from zero to 1750 rating is just as instructive if you assume he went from zero to 1650...
