Sequence Codes

My question is in regards to the various types of sequence codes.  It 
looks to me that with sales order charges, sales invoice charges, 
miscellaneous charges and sundry charges that they only allow up to three 
sequence numbers for each type (ex. 01-03, 11-13, 21-23, 41-43).  Is there 
a reason for this limit?  I have looked all over and have not been able 
find a reason for this.  Can anyone answer this question for me?

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