There's not a lot of great documentation available on what values change when an on-prem mailbox moves to the cloud. The full list is below, but it's important to note the following values since they are most often missed \ overlooked.
msExchRemoteRecipientType, previously null, will be set to 4
msExchRecipientTypeDetails gets changed from 1 to 2147483648
msExchRecipientDisplayType gets changed from 6 to -2147483642
Other values that change : legacyExchangeDN, homeMDB, homeMTA, homeServerName, ProxyAddresses, TargetAdddress