The original Jedec specification of DDR2 was as listed below.
How would you define DDR2-400 or DDR2-533 or DDR-667? are these failed versions of DDR2-800? Don't think so
It's just silcon produced for a specific application, in this case memory. Jedec sets the specifications for identifying the specific quality.
"DDR2 was introduced in the second quarter of 2003 at two initial clock rates: 200 MHz (referred to as PC2-3200) and 266 MHz (PC2-4200). Both performed worse than the original DDR specification due to higher latency, which made total access times longer. However, the original DDR technology tops out at a clock rate around 200 MHz (400 MT/s). Higher performance DDR chips exist, but JEDEC has stated that they will not be standardized. These modules are mostly manufacturer optimizations of highest-yielding chips, drawing significantly more power than slower-clocked modules, and usually do not offer much, if any, greater real-world performance."
DDR2 started to become competitive with the older DDR standard by the end of 2004, as modules with lower latencies became available