Caching is really up to the browser, and sometimes the ISP. And you might argue that anyone who goes a year without emptying their browser cache deserves everything that happens to them. But telling anyone, anywhere, that a file isn't likely to change in the next year is probably not something you'll do again in a hurry ;) Maybe on the internet equivalent of a tombstone-- but even then, what if you got the year wrong and had to call the stonecutter?
But if you type the original url for the old file, it appears on your browser.
For comparison purposes: My logs periodically show a request for an administrative gif that I stopped using pretty exactly a year ago. One IP continued requesting it until January (that is, three months after it was last visible in page code). A second IP hung on for about a month longer. A final IP is still
asking for the file several times a month.
:: detour to check most recent records ::
Frequency has dropped off in the last two months, and it's now only asking for three different files-- it used to be four-- but, still, we're talking about a year
after the most recent time the file was requested by any page, anywhere. Wasn't there an Agatha Christie novel on this theme?