Help using Names Ranges to sum data in rows across variable numbers of columns

Hello all - first post here, so hope it is a good one! I was reading the forum today and got a TON of great help, so wanted to thank everyone in advance because it was very useful. As I was reading though, I learned a few things, but then stumbled upon a couple things that stumped me...

Some background - I am well versed in Excel (currently using 2007) and have been using it for several years. However, I was never a progammer, and I learned everything on my own, so my technique could probably be described as "it works, but could be more efficient." Well, I am hopefully going to become a little more efficient now with your help....so on to my challenge!

I have attached a dummy workbook...two sheets, data and then a summary tab. I basically have sales data arranged by geography (in rows), and by time (months - in columns). Pretty self explanatory.

What I want to do is to have an efficient way to create aggregations of this data in my summary tab. I put together a simplified version in that tab, both with the approach I typically take (in red), plus two other methods I've been trying to figure out today using named ranges (green and blue examples).

I put notes next to each example and you can see my formulas...so my two questions are:

1) Generally speaking, for these types of aggregations, what is the most efficient way to tackle it? named ranges? using SUMIF, SUMPRODUCT, INDEX, or any array-based formulas?? (I need help with arrays btw)

2) After we figure out #1, because I will be using year-to-date aggregations, is there a way that I can dynamically have ranges updated each month with new data? Fore this, assume that new columns will NOT be appended, but I will simply lose a month of history...ie, if I have 24 months of data, then next month I will have 24 also, but one new month and lose one old month

Open to ideas and best practices!!! Thanks a ton and glad to be here!