I think your question goes to a particular problem in dovetails, and that is what to do at the scribe line at the very ends of the tails board, where the halfpins will sit. For the rest of the sockets on the tails board, you will be paring these to the line. But you are asking (if I'm reading this right!), what about the little end pieces--should I crosscut these to the scribe line, or pare them to the line?
What I have ended up doing is paring the entire baseline at once, using a paring block. It's one of the very few jigged cuts I make. Here's a link to a photo:http://www.traditionaltools.us/cms/index.php?name=coppermine&file=displayimage&album=29&pos=3
The paring block is about 2" square in cross-section, has to be dead square, and straight. It slides up and down on bolts through a base plate. There's a cleat underneath the baseplate that you can grab in an end vise--or else just clamp the baseplate to your bench. I position the tails board under the block so that the chisel hits ever so slightly shy of the baseline, like a shaving thickness shy.
What I have found is that if I have a crisp baseline, everything else will be fine right off the saw. But if there are issues at the baseline, doesn't matter how good your sawing is. For what it's worth.......