guessing that it's 'currently' in their week 20 production schedule. I imagine they don't 'absolutely fix' them that far in advance; hence use of 'current.'
For info: when I got mine in 2009; it was built considerably earlier than dealer originally expected (I know; I was lucky) and I think their system can move build weeks around to form suitable model batches etc which can result in alteration to that build week no. This is partly dependent upon what options you've selected and what's available, or running late, from their component suppliers. They need to try and support the 'just in time' production method as far as possible, so it makes sense for them to align similar vehicles in their calendar. At least; this is what my dealer told me when I was shown similar screen (but it was in 09 mind; so my memory could be a little vague).
There are folk on here who work in Dealers; so hopefully one of them will confirm / correct me as necessary.
Whatever the wait though; you'll enjoy it in the end (i.e don't pay too much attention to the extent of 'unhappy posts' on here or other forums as it tends to provide skewed view. Although I know some folk have had a few issues and some of those are significant; in my experience, and another 6 owner I know; we have not suffered the vast majority of the 'issues' some have). That 140 tdi is lovely engine too......