The only reason it was AZ instead of Merck was because the UK blocked the Oxford/Merck deal so they could force AZ to agree to “UK first” contracts.
And US companies ARE under an export ban.
So your point is?
The Oxford/Merck deal would have been with Merck KGaA, as far as I know. The US government would have had no means to apply export bans to a German-based company.