Class based networking has been obsolete for 3 decades now - and RfC 1519 was quickly implemented, so pretty much by the mid 90s any device looking up network masks by classes could be considered some broken legacy device.
RfC 1918 - which allocates the private IP ranges - came 2.5 years after the introduction of CIDR, specifies the networks in bit notation, and only references what the equivalent networks were in class notation as reference for people who have been asleep for a few years.