Allan - Here's one item that I don't see discussed in magazines much. I've taken apart my share of furniture from the age of handwork for repair - from colonial to 1830's or 40's or so. When I examine the rails on these pieces of furniture, the ends of the tenons are almost always quite rough, with some still showing the distinctive marks of a rough cross-cut saw.
When one reads some of the modern descriptions of hand-cutting m&T joints, the shoulders on the tenon are almost always laid out with a gauge working from the end-grain. Clearly, you have to have a square, fairly smooth end on the rail board to make this work. Yet almost none of the tenons I've taken out of their mortises on old furniture show this refinement.
So, this leads one to a conclusion about how M&T were made a couple of hundred years ago. Plaing end grain is fairly difficult with a wooden miter plane, and spiffy metal miter planes were at least 50 years away, and mostly stayed in London for the 50 years after that. So failing a nice, square, highly precise end on the rail to scribe a shoulder line in reference to, one can use the alternate method, which is to measure and lay out the shoulders based on a center measurement of the desired rail length rather than the overall length of the piece.
By doing this, you don't really have to have a precision cut on the two ends of the rail, nor do you have to plane this end grain. And rough-cutting the rail to length then measuring precisely between the two shoulder lines to establish the rail length is far, far faster.
There's one curious outcome of this thought exercise - you really can't do this very well without a folding rule. A tape measure just wants to flop over, and it's tough to hold the thing flat to get a good measurement. Because a folding rule is self-standing, though, it's really easy to mark the desired shoulder-to-shoulder dimension with a strike knife.
Funny how the tools available often set the work methods....