Yes, you are correct about the DS 213..
In theory, Synology's DiskStations are having numbers systematically..
The last numbers e.g. 2xx refers to how new the model are. For some time this number has indicated the year of production, but that system have failed as technology is moving faster and faster..
The first number(s) refers to the number of hard drive bays (e.g. DS 213 have 2 bays, DS 413 has 4 bays, etc)..
Last, the sign after the number refers to how powerful the NAS is, j (budget model), nothing (normal NAS), + (business level), etc..
NAS: DS 412+ with 4x3TB WD Red (RAID 5 + spare)
UPS: APC CS 500
Router: Cisco RW220w
Stuff: Retina MBP, iPad and iPhone..