What happens if I use a different android proration mode?

I have read in the docs that Reveuecat currently only supports IMMEDIATE_WITH_TIME_PRORATION for android upgrades/downgrades. However I wanted to clarify exactly what this means. If I were to use a different proration mode is it only the revenue/pricing that is reported incorrectly or would the expiry/renewal dates for the subscription/entitlement also be wrong?

For background we use the revenuecat event webhooks to issue users with our own premium entitlement and so we would need an accurate expiry/renewal date for the subscription to be passed in the webhook.

Many thanks in advance,

Lydia