For someone familiar with the boundaries of classful addressing, it is important to note that even though the RFC 1918 range of 172.16.0.0-172.31.255.255 falls in the traditional class B range, the block of addresses reserved is not a /16, but a /12. The same applies for the range of 192.168.0.0-192.168.255.255; this block is not a /24, but a /16. However, someone can still (and many individuals typically do) use addresses from these CIDR blocks and apply a subnet mask appropriate for the traditional classful boundary of the address.