### There is no way to add to an *already made* ability check

Any feature that adds to an ability check will include some phrase such as "the next ability check the creature makes" or "when a creature makes an ability check" or something similar because these bonuses are added *when the check is actually made*, not afterwards.

The rules on ability checks state:

> [...] To make an ability check, roll a d20 and add the relevant ability modifier. [...]

When the d20 is rolled, the check is made; after that point, the check has already been made and things cannot modify it unless they explicitly state that they can modify already-made checks.

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Stealth in particular states:

> [...] Make a Dexterity (Stealth) check when you attempt to conceal yourself from enemies [...]
> 
> [...] When you try to hide, make a Dexterity (Stealth) check. Until you are discovered or you stop hiding, that check's total is contested by the Wisdom (Perception) check of any creature that actively searches for signs of your presence. [...]

None of this suggests that you can add to the check *after* it is made; the modifiers are applied *when* it is made and if you want to apply later modifiers then another check (a *separate* check) must be made.