Crossgrade proof verification vs. sale deadline

I want to buy Cubase at the discount price before April 28 ends, but it took me some time to figure out my competitor crossgrade proof (from Logic Pro which has no serial number etc.)

Just started the process… and I’m worried that my proof won’t be verified in time for me to buy tomorrow. Should I buy at the regular discount price, and can proof of crossgrade refund me the difference retroactively?