MySQL - Binary Log File size growing more than the maximum limit

I have a MySQL 5.7 running on a Centos 6. I enabled Binary Logging and didn't provide any custom value for the maximum size of Binary Log in my configuration file. By default, the parameter **max_binlog_size = 1073741824** which is equivalent to 1GB. This means, once a binary log reaches the size of 1GB, a new file should be created. I observed in my server that all the binary log files are of different sizes with lot of contrast like 200GB, 165GB, 4GB etc... Why does this happen when the maximum size is 1GB for a binary log file? Is it necessary to mention even the default maximum size explicitly in the configuration file?