This web page from the dealer where I got my M4 notes the different model numbers and whether or not they can have a collapsing stock.
http://www.calssportingarmory.com/BenelliStockForends.htm
Benelli Shotgun Model #11701
- M1014 Limited Edition shotgun (stock will not collapse)
Benelli Shotgun Model #11703
- M4 Super 90 shotgun (stock will not collapse)
Benelli Shotgun Model #11707
- M4 Super 90 (stock will collapse)