As far as I know, the test the companies use if you try returning a boot saying it leaks is to take the dry boot and fill it with water and set it aside to see if any leaks out. If not, they consider it "water proof". In my personal experience, there is no such thing as a water proof leather boot and no such thing as waterproofing for leather. There are products that slow down the water but none stop it. Gore tex lined boots are water proof but it's not the leather keeping it out, it's the gore tex. After extended wear, the gore tex starts to break down at pinch points and creases. Waterproofing at that point only slows down the inevitable.
As for treating the leather, I've tried snow seal, mink oil, neets foot oil, vaseline, montana pitch blend, shoe polish, silicone, and just about every other water proofing goop I've ever found for sale. I've even made my own home made stuff. I don't even think of any of them as water proofers any more. They are leather conditioners with the possible exception of silicone which doesn't condition and resists water about the best. The real purpose of all the goop type stuff is to maintain or restore softness and flexibility after the leather has gotten wet and then dried.
If you try to test water proofing at home by running water in the sink and over the boot, it'll look like it works great. Too bad rain water acts differently. Rain drops will practically soak right in on some leathers that are supposedly waterproofed. Especially on something like suede with silicone treatment.
Also, when you go out hunting, you walk through brush and grass that works on your boots about like touching the inside of a tent during a rain storm. Not to mention all the little scratches and abrasions marks you get on the leather that lets water right in.
If you want water PROOF, use rubber boots.