When a company buys back stock it becomes "treasury stock" and is held by the company, usually losing its par value. The company may do as it pleases with this treasury stock, such as reintroduce it into the market it or use it as a form of compensation for goods and services received. If the stock is "retired" the shares are basically eliminated, the retired shares are removed from any A/S or O/S counts. In essence, shares bought back are good for the PPS but may reappear at another time, retired shares are good for the PPS and may not reappear at another time.
Hope, trust, and faith have no place in the stock market; let technical analysis be your guide to mighty profits.