Just think of it as the semi-final line as being sufficiently ironed out as to actually be more accurate than the final line.
Now, this raises a bugaboo about the "beat the closing line" worship that goes on in the forums these days, but I'll let the worshippers deal with it.
My personal testing shows the Friday night line to be a bit sharper than the close. I think it's because real squares don't start betting until gameday, generally, and the lines that haven't moved to their action yet.
IOW, if, say, a CFB total opened at 41, was at 43 on Friday night, and closed at 45, I'd say the 43 was the most accurate number.
But, apparently, that's just me.