On my hard drive, I have hundreds of data sheet .PDFs I have downloaded over the years. Every time I do a project, I make sure that I keep a copy of the individual parts data sheets, along with a scanned schematic...
Chances are that I would have most of the data sheets y0u may someday be looking for. Bad news, it has taken >25years to accumulate them.
Hmm... even if i have a huge amount of datasheet nicely stored in each and every project folder.. most of the time it's just quicker to use google! (that's if you have a decent internet connection, of course )
There are also some advantages to checking the most current version from the manufacturer. That said, I have a very useful datasheet for the venerable 555 that is no longer available. It is more of an application note. I have uploaded it here, but it may have been lost in the crash.