The E- prefix on STMicroelectronics part numbers was added as a designator for RoHS Compliant/Lead Free. However, as time went by and most of the stock was converted/purged to RoHS compliance; STMicroelectronics dropped the E- prefix since there was no longer any difference in the two ordering codes.
*Ex. E-L6202 is now just called out as L6202 and it is RoHS compliant.