I'm guessing but it might be the judges names on the top
and the scores they gave to the corresponding games.
Every book from about vol. 4 onwards gave the 10 best games (from the previous issue)
and the 10 best TN's. They usually gave the judges names and what game they awarded the points too.
As you can imagine a lot 'political thinking' went into awarding the points.
The first 'best game' was Fischer - Stein, Sousse Interzonal (1967).
Which is all rather strange because Fischer walked out of Sousse '67 and
his games were annulled...So in theory this game did not happen.
'Chess Brilliancy' by Damsky, an excellent book, goes into greater detail
about the games up to 1998 and the bias some of the judges displayed.
This really is a good book full of not just all the Informator games but nearly
every best game prize winner from other and older tournaments up to 1998.
Fischer - Stein, Sousse Interzonal (1967).