A buyback authorisation is permission, not a commitment. Companies announce a dollar amount and may execute slowly, or not at all. Executed shares are either retired or held as treasury-stock.
Buybacks are a steady bid in the market but they pause during blackout windows around earnings, which is one reason liquidity and support can thin out in the weeks before a report. Many buybacks only offset stock-based-compensation, so check whether outstanding-shares actually fell.
Example: a company earns $900M on 300M shares, or $3.00 of eps. It spends $1.2B buying 30M shares at $40. On 270M shares the same earnings give $3.33, an 11% increase with no operational change.
Related: treasury-stock, buyback-yield, outstanding-shares, tender-offer