Re: second half blind dovetail
When you knife a baseline (dovetail, tenon, etc.), you're forming the part of the joint that will be seen.
It takes only a small bruising of this line, the arris vanishes to nothing, to make it wavy (or worse) and show as a fault. I see this all the time on photos of joints that people post on forums purporting to be more or less perfect. Well, they're not. Mine probably look the same or worse, but I don't offer them up as the goal for which one should strive, either.
I think the old boys cut 'em and glued 'em. The more you futz around just handling the workpiece the greater your chances of damage that will show. The workpieces need to be clean and ready to be glued in place in whatever position they are to assume in the project or substructure of the project. Don't let is sit around, moving it here and there. Be ready to go. You're also probably better off cutting the joint a little lean and perhaps having to fill a gap or two with a little "joiner" than you are cutting one rich and having to do a lot of trimming to get it to go together without splitting. That kind of trimming almost always shows, up and down the joint, if you know what you're looking for.
Once you're cutting them consistently well, try to avoid the temptation of featuring exposed dovetails on everything you make. Move on to carving, veneering/inlaying or something else.