It’s as you say roughly, just that at a micro level the sMerits do not all return on a concrete date, but rather exactly 30 days after the sMerits were spent.

Say for example a Merit Source is appointed as one today, and is allocates an allowance of with 300 sMerits. Let’s say, for simplicity’s sake, he sends 50 sMerits every day for the next 4 days, and then stops sending sMerits. What will happen is as follows:

10/10/2021 10:00:00 UTC -> Merit Source sMerit balance: 300 sMerits
11/10/2021 15:00:00 UTC -> Spends 50 Merit Source sMerits  -> balance: 250 sMerits
12/10/2021 18:00:00 UTC -> Spends 50 Merit Source sMerits  -> balance: 200 sMerits
13/10/2021 11:00:00 UTC -> Spends 50 Merit Source sMerits -> balance: 150 sMerits
14/10/2021 15:00:00 UTC -> Spends 50 Merit Source sMerits  -> balance: 100 sMerits
<Now he stops sending sMerits>
10/11/2021 15:00:00 UTC -> Recovers 50 Merit Source sMerits  -> balance: 150 sMerits
11/11/2021 18:00:00 UTC -> Recovers 50 Merit Source sMerits  -> balance: 200 sMerits
12/11/2021 11:00:00 UTC -> Recovers 50 Merit Source sMerits  -> balance: 250 sMerits
13/11/2021 15:00:00 UTC -> Recovers 50 Merit Source sMerits  -> balance: 300 sMerits
<From here on, he won’t receive any more Merit Source sMerits, no matter how much time goes by (*)>

(*)Merit Source quota reassignment occur every now and then (perhaps with years in between). When this happens, the new allocated Quota could shift to a higher or lower threshold.