-R should be the order number when the DAE is ordered with an EMC rack and -N for customer rack install difference is most likely which rails and power cords get shipped  There are the sales order numbers - if you want to determine if there is a difference you need to look at the engineering part numbers like 005050149  then look it up in the Disk and OE matrix available from support.emc.com
I'm curious if there is any difference whatsoever between the "N" and "R" lines of VNX disk array enclosures.  They come in 15 or 25 slot, and some made specially for the VNXe series which end in E, but I can't find any documentation suggesting they're otherwise any different.  Can anyone shed some light on this? Example part numbers: V31-DAE-N-15 vs V31-DAE-R-15  V31-DAE-N-25 vs V31-DAE-R-25 V2-DAE-N-25-A vs V2-DAE-R-25-A V31-DAE-N-15E vs V31-DAE-R-15E V31-DAE-N-25E vs V31-DAE-R-25E  You get the idea...  Thanks!
VNX DAE compatibility