Just a thought here, the way I understand SID to work is that new/upgrade s/w is placed there for testing purposes then if all goes well it will move to Testing then Stable.
Now my question is, "What if I didn't update for a long period of time, say a month (I was on vacation) and an upgrade software was in Sid, tested, found to be ok, will it be 'removed' from SID, therefore I would no way I could upgrade nor would I know either?"
Am off my rocker or is this a possible scenario?
No, not quite right. First of all, your real concern is the packages installed or removed from your system, which is what apt is designed to manage. As I understand it (and others here know better than me), a package installed on your system from sid will not be removed unless/until it is replaced by a newer or alternative package that makes it obsolete (except during the transition of a set of related packages, which is why we have "upgrade warnings").
Second, the acceptance of a package into testing does not remove it from sid. If it did, there would be no possibility of having a sid distribution that would work, because it would never be a complete set of packages for the OS plus a desktop.
However, you are not completely off your rocker. A month is not normally a problem, but if you have a system that hasn't been updated for a couple of years, like I do (for a good reason), then that system really cannot safely ever be upgraded -- there would be tons of breakage and it would take longer to fix than a clean new installation/configuration would take.
I hope that is a satisfactory answer.
You should change your username to 'Speedy Gonzales' as that was one of the fastest replies I have received. Thanks, and it does make perfect sense on your closing comment.
and packages don't "move" to stable, that's why it is called stable.