Only the applicable retailations would stack - if you had three retaliate bonuses - one +1, one +2 vs melee attacks and one +3 with a range of 2:
If an adjacent enemy attacks with a melee attack, all three stack to a single 6 damage. If an adjacent enemy attacks with a range attack, the +1 and +3 stack, and if it is an enemy at range 2 with a ranged attack (or at range 2 with a melee area of effect attack), only the +3 will retaliate.
But - they will stack into a single source of damage.
It's important to ensure whenever you stack bonuses like this that they're the same 'category' of bonus, rather than just the bonuses themselves