Yes, serial number. My 4006 is also a TVC gun with a numerical component about 500 lower than yours.
A bit of history: For well over a century S&W had different serial number sequences for different models. In 1980 they adopted a universal serialization policy that used a single alphanumeric pattern -- AAA0000 -- that applied to all their models. This triple alpha/quad digit pattern allows for more than 175 million separate serial numbers. The company sometimes assigns specific alphabetic prefixes for particular production runs, so as serial numbers are used up, large gaps can remain in the complete sequence of available numbers.