A cell that is rested every 50 cycles for 2 days ages slower than a cell that is rested every 100 cycles:
The authors found that the recoverable capacity during a rest period depends on the current usable cell capacity (i. e., state-of-health: "UCC" on the chart). You can notice this above: the lower the UCC, the more capacity is recovered during rest periods, and the recovered amount at the same UCC levels are comparable for the two analysed cells.
The recoverable capacity also depends on the length of the rest period. There is a limit to how much capacity can be recovered which the cell approaches exponentially, so after 5 days very little capacity can be recovered:
On this chart, ΔC is the capacity recovery. UCC stands for "Usable Cell Capacity" relative to the capacity of a new cell; hence, black squares represent the recovery when a cell is almost new (50-200 cycles, rest periods every 50 cycles), red circles - when the cell is already close to the end-of-life limit in terms of remaining capacity (250-400 cycles), green triangles and blue stars - when the cell is already beyond the normal end-of-life and is cycled to death (450-800 cycles).
The authors found that the recoverable capacity during a rest period depends on the length of the period (as discussed above) and the current usable cell capacity (i. e., state-of-health), as you can notice on the chart above.
The authors found that the temperature at which a cell is rested doesn't significantly affect the speed or the amount of recoverable capacity.
When the authors analysed only the cells that were rested every 50 cycles, they found that the recoverable capacity roughly linearly depends on the lost capacity since the previous rest period, and that about 40% of that lost capacity can be recovered. However, this seems to me to be a false relationship because on the chart above, we can see that while the cell which is rested every 50 cycles recovers roughly 40% of lost capacity, the cell which is rested every 100 cycles recovers only 10-25% of the lost capacity.
Part of Cell capacity and Cell capacity fade.
 Investigation of capacity recovery effects due to rest periods during high current cyclic ageing tests in Li-ion cells and their influence on lifetime