I am comparing two large documents side by side. After trying different options, I found that the best way for me to do this was to highlight one data set grey, stack the two data sets, and then sort by one of the values. I then used conditional formatting to highlight the cells which were "unique" so that I could see what changed. I thought it was working great until I noticed a cell that the conditional formatting didn't catch. After finding others, I then used conditional formatting to highlight all the duplicate cells. Everything should be highlighted now (some unique, some duplicate). Yet half my document isn't highlighted at all. What gives?