Is unix predicting the end of the world?

I don't know if anyone has come across this before (couldn't find anything on google), but I came across a weird issue when checking account expiration dates: a date that didn't fit the format (Account expires : Feb 28, 235912). According to the man pages for usermod, the date format for 'usermod -e' is YYYY-MM-DD. This got me thinking what the maximum was.

I first tried entering only 9s until I hit the rollover to never (i.e. the argument rolls from a date to just never) and I got:

    # usermod -e 999999-9999999-99999999999999
    # chage -l test                                    
    Last password change                                    : May 16, 2014      
    Password expires                                        : never             
    Password inactive                                       : never             
    Account expires                                         : Dec 22, 2590218   
    Minimum number of days between password change          : 0                 
    Maximum number of days between password change          : 99999             
    Number of days of warning before password expires       : 7

    # usermod -e 999999-9999999-999999999999999
    # chage -l test                                    
    Last password change                                    : May 16, 2014      
    Password expires                                        : never             
    Password inactive                                       : never             
    Account expires                                         : never   
    Minimum number of days between password change          : 0                 
    Maximum number of days between password change          : 99999             
    Number of days of warning before password expires       : 7

Sort of Mayan Calendary, but I wasn't convinced. I knew I could go higher ....