Who actually does retention in a shop, and when
In almost every store that does this well, retention is not a marketing department. It is the store manager and two or three associates, working a short list on a fixed morning. Tuesday and Wednesday mornings are the usual slot, because footfall is low, the weekend billing has settled, and nobody is being pulled onto the floor mid-sentence.
The list is short on purpose. Fifteen to twenty five names per associate is the range most stores settle on, because a longer list gets skimmed and a shorter one is not worth the ritual. Each name carries three things: what they last bought, when, and who served them. The associate messages or calls, logs what happened, and the name leaves the list. That is the entire routine, and the discipline of it is worth more than any campaign the brand team runs centrally.