All - regarding CS2.4 production variants - my data is pretty sketchy. (It helps my puzzle-solving if you guys state your serial numbers if you can.) They ran from 2003 to 2012 when replaced by the 2.7. I have records of only 1000 pair, which interests me greatly. The 2.4 seems to be a bit of a audiophile darling, yet its sales are tied for lowest of any model. The SE may add 100 pair (or be included in the 1000 count.) It seems the progression from Lexington to FST / China is around sn 220 - 230. My personal experience along with other collaborators on this forum suggests that transition may partly account for the low sales volume. Reviewers and early enthusiasts would all have experienced the original Lexington units. The later (post 230) units to my ear lack the finesse, delicacy and ease of the originals. I wonder out loud if that discontinuity amounted to anything in the marketplace. It also seems that offshore sales were accounting for an increasing share of sales and that the USA market may have suffered via other non-product problems. Just guessing.
Rob says that Jim OK'd the FST production. But there are also documented stories of heated disagreements between Jim and Kathy as Marketing Director regarding various issues in that time-frame of the 2.4. Tim Tipton (long-term purchasing manager) ventured that Jim's ear was slipping. Cancer doesn't help bodily system performance.
The bottom line is that there is lots of room for improvement in the CS2.4 and with the considerable work already done on it and its forebearer the CS2.2, I suspect those 2.4 owners may be in for a sonic uplift if they so wish.