According to the application note of National Semiconductor, AN-1405, the difference is listed below.
RMII Spec. Revision 1.2
CRS_DV will toggle at the end of a packet to indicate deassertion of CRS.
RMII Spec. revision 1.0
CRS_DV will remain asserted until final data is transferred. CRS_DV will not toggle at the end of a packet.
