^while it’s not impossible nor illegal, it’s highly unlikely; but even if it were the case, it’d still be better continuity to be in an IB program that has some added lessons, than start 12th grade in a completely different system (with no guaranteed access to APs to boot).
The US system DOES have some quirks, in that some States or districts require both English and History of the Americas at HL, which severely reduces strong STEM students’ ability to choose classes appropriate to their future major, sometimes forcing them to choose to have 4 HLs/2 SLs so that they have MathHL and another science HL.