A bit of book keeping is necessary to match up the entries in the two tables.

Since the first 4 entries (at indices 0 - 3) of the kernel's table describe the tasks, the entry at index 4 of the kernel's table corresponds to entry 0 of the pm's table.

Since NR_TASKS is the number of tasks (4), in general,

kernel table                          pm's table
proc[k + NR_TASKS]  corresponds to    mproc[k]