Once the visas come down to EB2, they are applied to the EB2 category as whole. There is no special class of spillover visas.
Now within EB2, there are specific rules for granting the visas. They are same rules irrespective of whether there is a cut-off date for the category or not, and whether the visas are coming from regular quota or from spillover.
The rules within the category are always the same.
Hence USCIS changed the spillover rule in 2009.
Earlier they were doing Eb1ROW => EB2ROW => EB3ROW fall down and no fall across. Now they do it EBROW => EBIC fall across within each category and then a fall down EB1 to EB2 to EB3. This is a category fall down.