I don't know how common it is, but it doesn't sound like good practice. In every independent school in which I worked, updated salary scales were published in the January before the September in which they came into effect. Small prep schools, perhaps struggling with finances in the current climate, are a different matter, though. I'd ask your longer-serving colleagues if this is normal at the school concerned. On the face of it, it sounds as though they are waiting to see how many pupils are still signed-up for next term before committing themselves to salaries. If this is not standard practice at the school concerned, it would ring warning bells of possible financial difficulties for me.