Extend or book again

A long-stay rate is priced on the length of the stay, not on the calendar. Extend 21 nights by 14 and it is one stay of 35, which reaches the threshold — the lower rate then applies to all of it. Book those 14 separately and they are two stays, both under the threshold, and the final cleaning is charged a second time. The same nights, several hundred euros apart, and nothing on a booking page explains why. One assumption is named rather than hidden: we model the long-stay rate applying to the whole continuous stay, which is the usual shape for furnished long stays. Some contracts apply it only to the nights past the threshold. That changes the answer, so it belongs in the result and not in the small print. The deposit is shown separately — it is held, not spent — though a second booking means it is held twice.