I read in a review that the SE patches are "cut-down versions of their Vienna Instruments equivalents with fewer velocity layers and samples spanning a tone rather than a semitone."
If you look at www.vsl.co.at/en/211/1343/1289.vsl, it says "The Standard Library of a Single Instrument offers slightly more articulations than the same instrument included in the Vienna Special Editions. By adding the corresponding Extended Library, all Single Instruments become full-fledged Vienna Instruments, offering the complete samples and articulations on par with the ones of the big Vienna Instruments Collections."
Since the Single Instruments are potentially on a par with the fully-fledged Vienna Instruments Collection, one can assume they have more velocity layers than SE. HTH!