During construction a house is opened by a great many people. A site foreman, the plumbers, the electricians, the tilers, the painters, the flooring team, the cleaning crew before handover, and whoever let each of them in on a Saturday. On a development, that access is frequently managed through a builder's key or a common cylinder across a phase, because managing individual keys across dozens of half-finished units is impractical.
None of that is improper and all of it is normal. What is not normal is that the cylinders often stay exactly as they were when the buyer takes occupation. The keys handed over at handover are genuinely the buyer's keys; they are simply not the only ones that were ever cut, and there is no record and no realistic way to build one after the fact.
So the single most useful thing anybody moving into a new home here can do is change the external cylinders before the furniture arrives. It is inexpensive, it takes an hour, and it is the only step that converts an assumption into a fact. That is straightforward lock change services work and it is the most common booking we take in this suburb.