You can use KCL at the ground node.
First, because in many circuits, the "ground" node is not actually connected to earth ground or to anything external circuit at all. It's just another circuit node that we use as reference for measuring potential at other nodes in the circuit.
Second, even when the circuit is externally grounded, there is the cut-set form of KCL. A cut set is any set of branches of a circuit that, if they were cut, would split the circuit into two disconnected circuits (but if any one of them were not cut while the others were, the circuit would remain connected). The cut-set form of KCL is:
KCL (cut-set law) For all lumped circuits, for all time t, the algebraic sum of the currents associated with any cut set is equal to zero.
(source)
What that means is, if you consider all the places where your circuit connects to earth ground, the net current through them is zero. So therefore KCL can be applied to all the places where other elements of your circuit connect to the local ground node.
Some time ago, I answered a similar question here.
The first sentence, which is an echo of commenters here is:
Unless there is a compelling reason otherwise, I use the same ground everywhere.
The Maxim application note is targeted at mixed signal integrated circuits, where, unless you take precautions, the digital and analogue currents will overlap, and the usual method of managing this is to tie the effective digital and analogue grounds is at a single point (usually beneath the device).
Understanding how the currents move in the plane(s) is the key to good signal integrity, and the general rule of putting the sensitive circuitry furthest from power and the noisy stuff close to it is a good rule of thumb, but every design needs to be analysed for clean power and grounds (the return path which is the 50% of the power that does not seem to appear in a schematic but is just as important, of course).
[Update]
Under very limited circumstances, a split plane may be appropriate. There is a trade-off of effort vs. return on that effort. In an ordinary mixed mode system, I would not split the planes.
The example was a specific design that had very high eddy currents on the LEDs where it was easier (and appropriate) to split the planes to prevent those eddy currents from inducing into the other LEDs. The grounds were tied together at the primary power inlet to the board.
I think my primary point on where things are placed is that sensitive devices should not have return currents from other devices under them. In a system with high speed logic and ADCs, I would put the ADCs at the end of the power path so that the digital returns cannot interfere with the measurements.
Perhaps I had not made that as clear as it could have been.
HTH
Best Answer
I think also A is better in order to avoid other signals return gnd path going through your module. But up until now I'm using "C" image and I've not anticipated any kind of problems.