337 production for 1940 quoted as roughly 130,000 by Law and 145,000 by Jensen and Kuck in the old KCN articles. It is true that a 337 dated 1939 is one of the rarest K98's - with production probably around 10,000 and very few known in existence. I know it is regarded as the 'holy grail' of K98's on the k98kforum.
BSW for 1937 produced 25,000 rifles and in 1940 50,000 rifles, again not common rifles to say the least. However, more BSW 1937's pop up than 1939 337's. I have yet to see a 337 dated 1939, but I have a 1937 BSW dated 1937, ordered a BSW 1937 from Lever on behalf of my friend and now they have another one in stock. So, within two years at least 3x BSW's dated 1937 have been on the Canadian market; all of which in RC format. For some reason they seem to have a decent survive-ability.
The rarest of the rare is the lone BSW 1936 (held in a Russian collection) with only one reported.
Lever does have nice K98 rifles, but sadly for buyers, they knew what they had and requesting maximum profit. Heck I bought a swp45, S/27G and that BSW on behalf of my friend all in one morning from lever. We paid a hefty fee, but ended up with some rare-uncommon rifles. I know that on the K98Kforum there are only 17 reported S/27G's, so that is pretty cool, especially as production was only at roughly 3-4000 rifles, even if RC format.
I have another two cool rifles to unpack from Lever sitting in a box, hopefully I will have time to enjoy them today.