15% is most on a magic prefix. 35% is most on a suffix. That's 50%. 62% would imply either 2 pre's or 2 suf's, which of course will not happen on a magical "Fortuitous Amulet of Luck", nor are either of those pre/suffixes available on a rare.

Prefix: http://www.battle.net/diablo2exp/items/magic/pre.shtml

Suffix: http://www.battle.net/diablo2exp/items/magic/suf.shtml