Codes like E1 , E2 , or ER often denote specific engineering revisions, stepping levels of the chipset, or manufacturing line identifiers. These suffixes tell technicians if a board has received specific hardware patches or updates during its factory production run.
The string "01 21 b6 e1 e2" likely follows this same pattern of regulatory codes. The "er" that appears in your search may be a partial reading or a mistaken inclusion from a similar board marking. intel desktop board 01 21 b6 e1 e2 er new