Heres' my opinion, and how I'd value that set, since you asked.
The big 'prizes' in that collection are the mint condition 51OT, 25OT, 858OT, and the case itself. The 61OT (a favorite of mine) are less-common, but don't usually sell at premium prices. I'd figure $75 for each of the 4 "goodies". Those would come to $300-ish, leaving $350 for the remaining 11knives, or $31 each. Some of the others are worth less than $31, and some a bit more than $31, but $31 would be a fair average.
So yes, I'd say you did a good job. Thumbs Up, and congradulations!
Could you recover the $650 by re-selling the knives individually? Likely. But IMO they're worth more as a matched set with factory display than seperated. The problem is, when you sell more valuable items many casual e-Bayers and even hard core collectors are priced out of participating.
-Bob