igmaty - the CS2.3 was introduced december 1997 and had a minor XO tweak November 1998. Thiel’s serial numbers always began with #1 and 1/2 were the first pair, etc. My notes say about 2750 pairs were made, so numbers would top out about 5500. The coax was updated some time in the product life which necessitated adding an 8.5 ohm resistor and 3uF cap. That change came February 2001. Try Rob Gillum about the particulars of how to identify if you have early or late 2.3s. Once you get oriented, there is substantial / qualitative sonic improvement to be had via relatively simple crossover component substitutions.
First get them up to speed and have fun listening.