Well that was strange
I bought the S8 only a few days after release then a week later got the S8+ and gave the S8 to my wife
My S8+ got the May update about a week back the wife S8 only got the update today and both are international versions
Makes no difference that both are international versions. Indeed there is no such thing as just a single international version either as every country has a different CSC code and it's therefore seen as a separate device, so Germany is seen as a different device as France even if both are bought unlocked, carrier unbranded.
Likewise the S8 & S8+ have two completely different hardware identifiers and are treated as two completely different devices.
And finally even if you have two devices that actually are identical and from same region this sharing same CSC, they have different IMEI's and Samsung likewise rollout the updates in batches to IMEI ranges so the two phones even if sharing CSC wouldn't necessarily get update at same time either.
It's just another reason why android updates generally are such a mess.