Assigning gets really, really complicated at the WC. Some refs don't get early games because they are the bottom tier and are only going to get a game with little impact, if at all. Some are not actually expected to get a game, though who those are is often not clear. Sometimes the top tier refs don't get a game early because there isn't one that the assignors think is worth "spending" them on. And you add, mostly, confederation neutrality: in general a referee won't be assigned to a game if one team is from his federation. (That is being breached for Argentina-Poland, but is rare, and may well explain why the assignments were late getting out.) Rs also won't work a game in the Group their home country plays in, or that is seen as affecting who their team will play next (e.g., from the group their group will play in the first KO round). And sometimes a ref won't be given a game that is more likely to get messy because the powers that be don't want to risk that ref being stained by a bad game and hard to use in the quarter final or later. Oh, and you can mix past experience with the ref, as well as geo political messes, and it all adds up to a very complex logic puzzle.