In the episode, Wendigo, we see a page from John Winchester's journal about wendigos and on the opposite page a bunch of random symbols. Later on, in, I believe, Faith, Shadows, or Hell House (when they look up a symbol) they find that symbol on a scrap of paper attached to the page next to the wendigo page. They then look at each other, realising they've found the symbol, and their dad noted it down.
Have they been organising the journal? Or is this an error? It seems a fairly rookie mistake to me, if it is such an error.