Accounting request duplication check

[rosect190 at yahoo.com]

I recently noticed that the freeradius server checks duplicated requests by comparing length and authenticator.
This is fine with authentication request because the Authenticator field in Access-Request is a random number.
However, in Accounting-Request, the Authenticator is MD5-hashed with same info, unless length is different (assuming same other attributes info.). If length is the same, this way, there is basically no duplicate packet check. 

Is my understanding correctly?
Thanks for your attention!