It is suggested that chances to see through a veil are determined by the number of units veiled multiplied by the number of warlords looking. In Page 107Erf-b1-p107 there are 11 warlords looking for "30 or so" units giving around 300 chances. A direct multiplication would give 330 chances for that particular stack to find 30 veiled units.
Another explanation for "330 chances" is that each warlord rolls once against each veiled unit that it might see. If the roll is a success, that warlord sees that unit. The chances of winning that roll would therefore still be unknown.