The excel error is just letting you know that the formula is different in one cell than it's neighboring cells. Each of your formulas is looking at a different size data set. It's just trying to help you in case you intend them to all have the same formula. Placing $ in front of the cell column and row pointes should fix it.
OK, I looked at one set of data that I did manually and I ended up using 73% of the data. I'll try to play with STDEV and the other excel functions tonight.