How and when do CC benefits changes affect existing cardholders?

[LovinChicago]

When a credit card issuer changes the benefits associated with a particular card they are obviously immediately available to new applicants. But when do existing cardholders get to use those benefits: (a) immediately, or (b) after the next cardholder anniversary and payment of the annual fee?

As an example, AMEX Green added the full $189 CLEAR credit back in November. Would a person who already had the card as of the time of the announcement immediately get to use that benefit as of the effective date, or would the benefit not go into effect for them until their next cardholder anniversary? Thanks!

[Remedios]

If it's been added to existing accounts, it should be available immediately upon addition. 

[Anonymous]

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@Remedios wrote:

If it's been added to existing accounts, it should be available immediately upon addition. 

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Right, you just need to distinguish actual "increase of benefits on the card" with "enhanced benefit as SUB".  So the latter includes  the current chase freedom unlimited  earn 5% cash back on grocery store purchases (excluding Target® and Walmart) on up to $12,000 

which obviously doesn't apply to existing card holders