Tables 2000000053 and 2000000054 contain references to the virtual table "SID - Account ID". The contents of this table are calculated on the fly in memory.
If you want to find the value in a SQL query, you should call the function select suser_sname( SID ) in SQL server. Note that the SID in the parameter is a binary representation of the SID, and in NAV you are getting a string representation of the SID.