Also, that is a great way to use that information @DanWL. I might just end up tracing WL growth that way from beginning until the end.
@Ben, Well I neither feel that the player base have grown soo much... but then I think about the huge increase in number of trolls on the forum. Now that has changed a lot.
You wouldn't even need to do a lot of scraping to get a decent graph of this, since it would be an XY plot. Just sample a bunch of players (even just from those posting in the forums would be a good start), find each (ID, Join date) pair, and plot it. If your hypothesis is correct, then the result should be a strictly monotonic graph, and it would give a lot of visual information about WL growth, including spurts and trends.
I bet even as low as 50 (relatively random) samples would still give a good rough graph. Certainly knyte's existing data contains enough information already to produce a very good graph, esp. considering there are clans containing very old players and ones containing very new players.