I was recently watching a stream with a Black Pudding attacking a player. The DM missed the player but still had the dissolve effect happen to their armour.
(MM p. 241) Pseudopod ...[snip] Hit: 6 (1d6 + 3) bludgeoning damage plus 18 (4d8) acid damage. In addition, nonmagical armour worn by the target is partly dissolved and takes a permanent and cumulative -1 penalty to the AC it offers. The armour is destroyed if the penalty reduces its AC to 10.
This differs slightly from the more clear verbiage on the Grey Ooze, where the corrosion is clearly still part of the Hit sentence:
(MM p. 243) Pseudopod ...[snip] Hit: 4 (1d6 + 1) bludgeoning damage plus 7 (2d6) acid damage, and if the target is wearing nonmagical armour, its armour is partly corroded and takes a permanent and cumulative -1 penalty to the AC it offers. The armour is destroyed if the penalty reduces its AC to 10.
Since the Black Pudding is a higher CR creature, it's not outside the realm of belief that it was intended to be a more dangerous effect, and since the verbiage is actually different and part of a separate sentence it raises a bit of confusion as well.
Does the Black Pudding apply this effect on hit, or on attack?
If it's also on hit, is there any concrete reason why the language on two creatures in the same Monster Family, only two pages away from each other is different?