Walther Numbers
You may not get a reply from Walther as its quite complex for them to trace, as manufacturing and marketing is at two different sites, Ulm and Arnsberg, and I know they are always very busy.
If not, I can tell you it's certainly not a prototype, or first off production, and your LG400 is unlikely to be anything special and would have almost certainly gone to a UK importer, unless its a grey import.
Walther numbering has always been a bit strange, generally just numbers with the initial number or numbers indicating the model, but again some variances. My LG400 was one of the first into the UK in 2011 the first year of production, and its number 40566 so probably 566'th made, maybe! My wife's LG400 from 2013 is 42589, and that is a one off special, a LG400 expert system in a Wood Junior stock, Walther have never made vast quantities of their match guns.
In recent years Walther changed the serial references to include prefix letters, I believe model specific, hence your is KBA, so yours is from recent years, and I suspect just luck on the number, could have been 0007, but still no significance!
My wife does have a pre production KK500 and that number is 500*** , while my KK500, a later 2019 one is KFA 21**
So an interesting number, but I doubt any significance other than just being lucky to get it, regardless they are a great rifle so enjoy it!
Have Fun
Robin
Walther KK500 Alutec expert special - Barnard .223 "wilde" in a Walther KK500 Alutec stock, mmm...tasty!! - Keppeler 6 mmBR with Walther grip and wood! I may be a Walther-phile?