New 990 Form Type Meanings 
 Returns having Subsection code C3 
    Code            Meaning 
990                     990 
990EZ        990EZ 
990R          990 Rescans 
990ER        990EZ Rescans 
990A           990 Amended 
990EA        990EZ Amended 
  
   Returns having Subsection code other than C3 
    Code            Meaning 
990O          990 Others 
990OA        990 Others Amended 
990OR        990 Others Rescan 
990EO        990EZ Others 
990EOA      990EZ Others Amended 
990EOR      990EZ Others Rescans 
  
The term "Others" refers to any 990 with a subsection code not equal to '3'. 
The term "Amended" indicates the return is not an original filing but an amended return. 
The term "Rescan" indicates the return was rescanned after tax processing made changes to the return. 
A column in the .dat file (the one right after the 990 type code) shows the Subsection code values.   For all the C3 types, the subsection code should be 3.  For the Others types, the subsection code should be anything other than 3, including nulls.  Nulls indicate the Subsection code was left blank by the taxpayer, or has yet to be determined by IRS tax processing.  We scan before that determination is made.
  
From and email by David K. Hamilton, IRS, Ogden, UT.