Technically there was no level cap on Crission's Pixie Strike or Song of Twilight, but mobs above level 55 were immune to all resistible mezzes, so they effectively had a level cap of 55. However, they could still land on 56+ players.
The link you posted actually shows that it was obviously not capped at 40 since someone claims they could mez mobs in Hate (which are level 49-51 except for the pets and the bosses).
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Project 1999 (PvE):
Giegue Nessithurtsithurts, 60 Bard <Divinity>
Starman Deluxe, 24 Enchanter
Lardna Minch, 18 Warrior
Project 1999 (PvP):
[50 (sometimes 49) Bard] Wolfram Alpha (Half Elf) ZONE: oasis |