I've never heard of peanut butter going bad in the refrigerator. The high oil content makes it last pretty much forever. I don't see how homemade would be any different from Trader Joe's all-natural in this regard -- sometimes it takes us a year or so to go through a jar.
I believe it. I rarely eat the stuff. I'm hoping the homemade will go faster. Since there's less sugar in it, I'll be more likely to use it in cooking: salad dressing, sauce for noodles, dipping sauces, etc.
The high oil content also makes it go rancid, which makes it taste "off." Buy a new jar and compare it to the 10-month-old jar you have in the fridge, and you will be struck by how old and off the old jar tastes and how fresh the new jar tastes.