Historically, the Romans used both IIII and IV for 4. The subtraction notation was not standardised until much later. There are plenty of instances of IIII on t

Historically, the Romans used both IIII and IV for 4. The subtraction notation was not standardised until much later. There are plenty of instances of IIII on things like coins from the 17th and 18th centuries (though not that much for dates, for which a shorter notation was preferable), and examples dating back to Ancient Rome. So, it was at worst old-fashioned but never erroneous.