Ann: Daily share buy-back notice - Appendix 3E , page-4

re: Ann: Daily share buy-back notice - Append... last BB notice was for purchases on 2 dec leaving 1,158,203 shares left to purchase in order to complete BB.
Are they obliged to complete BB before commencing new $20m BB ?
Going on volume since 2 Dec AMU arent the only buyers in the market.
They seem to me to have done a fair job of managing the BB without paying too much but at some point surely the register will begin to tighten up and AMU will have to pay more, especially given that none of the substantial holders have been sellers so far