Wooooo legal constraints! Correct, we are not allowed to present more than 25 players to you at a time. For your specific use case, is there a reason why you don't just pull the rosters and ask for the weekly stats at the same time? We do have the ability to ask for both team stats over certain intervals and player stats within teams over certain intervals. Kind of like...
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http://fantasysports.yahooapis.com/fantasy/v2/team/223.l.21821.t.9;out=stats;stats.type=week;stats.week=10/roster;week=10/players/stats;type=week;week=10
(one of my teams from last year, but hopefully you get the idea)
It seems much more straightforward to let us do the work for you instead of having you pull down an entire database of players and stats for all of them.