To clearly define, "Duplicate Account" bans arise when the IP address an account is connecting to the servers on is detected to have bans associated with it. So for example, a cheater gets banned on a throwaway alt account, his Steam ID and IP address are banned, so if he tries connecting back to the servers on his main he will still be on his same IP address and therefore get that account banned to.
You don't need to worry about anything if you aren't trying to use alt accounts to avoid punishments though, as that is the only instance we punish specifically for alt usage.