Keep in mind,we keep emphasizing that the quality of the packer will have a lot to do with the final product.Briskets are a mite independent.
I've observed,that a perfect brisket,the first time out,happens about as often as a perfect olympic dive, from a cowhand, from the 10 meter board,into a cattle trough.
Next,I'm not sure I really know what a "deckle" is,how to find,season up,-or cook one.
After that,I reckon I been around cow cookin' since I learnt how to stand up and pee,and gasoline in south OK was $0.021/gal
I've seen maybe a dozen packers,from US of A cows, come done at 193*.
As you cook enough packers,you find that the flat is dry/tough and figure that is ALWAYS a sign of overcooking.
I've been taught by some pretty fair brisket cooks,to just keep on cooking,until the probe-or a two tined meat fork,will go thru from top to bottom,like warm butter.
Sometimes, you might hit 210*
We all worry about ruining/wasting a $20 chunk of meat,but the experience pays off.
Think what a cook costs,especially if you drove 1500 mile,each time,to make it.
Worst case, we make a Tex-mex dinner,or a fine skillet of hash.
Now,if we're talking about the point,some is done,the same time as the flat,and makes great slices.Others, might take three more hours,go to 215*,and then chunk it up for the "cooks candy".
Keep cookin' and takin' notes,and these good cooks will get ya there.
Now,I'll get outa here,before they accuse me of makin' a Smokin' post.