Time relationships in a school announcement

An original classroom exercise compares three messages. The first says, We have used the old hall since September andwe still use it now. The second says, We used the sports centre last Friday while the hall was being repaired. The third says, If the repairs had finished earlier, we would have returned to the hall last week. A learner changes all three main verb phrases to the simple present because the messages concern the school. Another learner notices that the messages distinguish a continuing situation, a completed event andan unreal past possibility. The teacher asks for a meaning-preserving explanation rather than an invented examination rule. The exercise is about English time and aspect. It does not establish a real school calendar or claim that a particular verb form is correct in every possible context without considering the speaker's intended meaning.