We might be using different definitions of the word retire, but I would ask how you know those share can't be reissued. I believe they go back into the pool of unissued shares. Don't see why they would not. A company can't issue as many shares as they wish, the number is restricted by their charter and amendments. The total number of shares Apple is authorized to issue, I have no idea. Do you know how to find that number?
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You might mean something different when you refer to retired shares or retiring shares, but I'm using the terms as they are typically used - e.g., by companies in SEC filings and consistent with SEC regulations. Here's a basic definition of retired securities.
There's a difference between retired shares and treasury shares; they are accounted for differently and subject to different rules. What you were describing earlier (in post #167) sounds more like treasury shares. You can probably do a search to learn more about the differences.
To answer your question about how I know those shares can't be reissued (though I didn't say that in my previous post), it's because I'm familiar with the SEC regulations. Retired shares can't be reissued. And Apple has been retiring the shares which it's been buying back. We know that from its SEC filings.
As for the number of shares authorized to be issued, it's also referred to in various SEC filings. It's been 12.6 billion (split-adjusted) for quite some time. At the time of Apple's IPO it was 8.96 billion (split-adjusted), but it was increased at some point in the 90's to 12.6 billion. So, as I indicated, Apple can issue new shares. That would be the case whether it had recently bought back (and retired) shares or not.