66 blocks do not have 66 rows. They have 50 rows, generally. Sometimes fewer, like 32 for a 16-pair cable, or 12, for a 6-pair cable.
66B25 and 66B50 are the last iterations of the blocks that are bigger. (More space between rows than the "M" [mini] blocks do, so they are physically taller, and take more room on an MDF.)
M blocks come in 25-pair versions, (4 pins across each row, all connected) and 50-pair versions (two sets of 2 pins in each row, left side insulated from the right side.)
My suggestion to remote the outputs from the shoebox to an out-board block has little to do with electricity, and more to do with physical convenience and trouble avoidance. It was said to rebut the notion of trying to cram 10 cables (wired using the loop-through method) into a shoebox.
After having wired approx 10K key sets in my lifetime, my method is to provide a source block (generally a 66B25, for ease of counting and 5 useful outputs) and to provide a 66M-50 split block for every 2 key sets. Then, cross-connections are run to take the features from the source block, and assign them to the key sets.
If you do that once, you have accommodated 10 sets. You can do it 4 more times, from a shoebox internal block, and energize up to a total of 50 key sets. More than a sane collector would want hooked up at one time. I, of course, am not quite sane, and have 20 or so key sets hooked up right at the moment.
