The tap conductors do not extend beyond the switchboard,
panelboard, disconnecting means, or control devices they supply.
I did read 240.21(B)(1)(2), but thought it meant that, after the tap conductors enter the panel (that they are supplying), that they do not extend beyond that panel.
If in fact the entire length of the tap conductors must be contained within a single panel (in essence, restricting 10' taps to being no more than jumpers within a single enclosure), then what are we to make of 240.21(B)(1)(3) ?:
"Except at the point of connection to the feeder, the tap
conductors are enclosed in a raceway, which shall extend
from the tap to the enclosure of an enclosed switchboard,
panelboard, or control devices, or to the back of an open switchboard."
I think 240.21(B)(1)(2) needs clarification.