I have 2 sets of original CLS. The interface box serial on one pair is 2634 and was manufactured in 87. The other pairs interface box serial is 3482 and was manufactured in 88. The interface box serial numbers are usually consectutive. I am not positive, but I believe that the first digit in early ML serial #'s is the year of manufacture. 0 = 85, 1 = 86, 2 =87 and 3 =88. There was a manufacturing code key posted here for models from 89 on that use the current alpha-numeric serial #'s. As mentioned, a quick call to ML will ID what you've got.