Yes this, there is no reason why this detail would be in the public record. Since the owner was selling his house, it would hardly be unreasonable that he would engage a cleaner to come periodically to make sure the interior looked its best.
SJL's colleague MG went back to 37SR twice, first with a female colleague. We have no concrete idea if he physically went inside or not because the only public record, AS's book, is very vague on this. One assumes that he did not go inside, since later that day the police did go inside and the next day a forensics team checked it, and found no evidence that SJL had been inside (no prints or signs of a disturbance). It does not take a "big red key" to force a lock even if there was no spare set of keys, so the police gaining entry with no visible sign of damage viewable from a photograph taken at a bit of distance is not evidence that SJL did not take the keys.
However, as there was only one set of keys in the estate agent, it would have been an instant red flag to MG if SJL had not taken them to the viewing.