If that’s the case, then travelers coming from States that don’t mandate IIS participation are going to have a tough time proving vaccination status. The various COVID-19 passport apps pretty much all depend on the QR code which is part of the digital record.
Both of these screeds are from leftists who are whining about the impossibility of verifying vaccination, but they are accurate in so far as what the system is:
https://www.theatlantic.com/health/archive/2021/05/america-covid-vaccine-honor-system/618891/
Even NY’s system doesn’t prevent people from sharing screenshots and it only can track NY shots and then only those who haven’t opted out of the State database. (Something I recommend everyone doing if you are in an Opt out state.)