Hi,
I am Jürgen from Germany.
I am a member here, because the Flickr stats told me that sometimes my ebay charts for Pentax-K lenses are linked from here.
https://www.flickr.com/photos/ossy59/18855799296/in/album-72157603469902678/
And here I have the chance to comment if necessary.
I startet collecting the price data on Ebay Germany when I have bought my first DSLR Pentax *istDs. When I had found "my" lenses, I collected the data for my friends. And with the years, then because of users in german forums, I thought I should make charts to see how it goes on with Pentax (a few times it looked like Pentax will no longer exist ...)
Today there are charts for 280 PK-lenses (I have data for more than 400 different lenses). For this charts I opened very one of the nearly 70.000 ebay auctions. And only when the photos and the description are so, that I would buy the lens by for myself, then it becomes a part of my charts. A lot of work, but I only could give advices for my friends when I am more or less shure that they will receive a "good" lens.
Unfortunately not one software, also not the ebay search function, can evaluate the lens. So it´s all done manually, except the raw data base for an easier sorting for excel.
I still have to go to work, sometimes overseas, and that´s the reason why I often have not the time check, collect and make updates.
But I think the charts are still good for a quick overview.

Today I own 50 different lenses, 7 old non digital Pentax SLR - my first one was a ME-Super in 1982 -, 11 digital SLR from *istDs to K-3.

Greetings from Jürgen, mostly called Ossy
(sorry, me english is not the best. I have learned it for 5 years, but I left school in 1974, and forgot a lot)