When an assignment event takes place it must first be executed (such as a contract signed between two parties).  This is the effective date of the assignment.  However, there may be a delay before the paperwork is filed and recorded by the governing body (thereby making the data available to AcclaimIP).  Both dates are tracked in AcclaimIP.  

To query patents by their most recent date of recordation of assignment events use the ANRE_REC_DT field code.  Whereas the actual effective date of the assignment is recorded in the Assignments tab of the Document Details window, the ANRE_REC_DT field data is in the Legal Events tab.