Correlation
Use the correlation feature to attempt to match each person being granted an Account entitlement to an existing target account, prior to creating a new account for the person.
To get started, Configure correlation.
Correlation works by matching a chosen field in the Person schema (Person Correlation Field) with a matching field in the target account schema (Account Correlation Field). Then, in the Account Create script, you use the properties in $actionContext.CorrelationConfiguration to check whether an account with a matching value already exists in the external system. If yes, instead of creating a new account, you correlate the person with the existing account.
In this case, when the account create script finishes, the Account Update script will immediately be run with $actionContext.AccountCorrelated = true, so you can update the correlated account as needed. When this happens, there will only be an Account Update notification event, not a Account Create notification event.
Tip
The Person aggregation feature is loosely related to correlation. The difference is that whereas correlation matches a person object to a target account, person aggregation matches employees from raw personnel data to person objects.