I'm not sure about now, but I believe they used to give out "tickets", (basically certifications made by the Steam servers that say "This login or whatever is valid!"), that lasted for like a month each. This made it so that you could play offline without having to first be online, as it would identify your locally stored ticket and make sure it was valid, which would work offline up to a certain point - in most cases, you'd probably have a week or two of being able to play offline - sometimes longer, and unfortunately, rarely shorter if it was closer to expiring.
...But, judging by all these complaint posts, it seems as though they might've changed their system. Don't know why they'd do that - did people figure out how to counterfeit them? Either way, I don't think they should've changed their system, as people no doubt have found a way around it if that is the case...It's been a while since I've had to use offline mode right off the bat, but in the few cases where I've had no internet from a cold boot, I've been able to use it just fine.
...But, judging by all these complaint posts, it seems as though they might've changed their system. Don't know why they'd do that - did people figure out how to counterfeit them? Either way, I don't think they should've changed their system, as people no doubt have found a way around it if that is the case...It's been a while since I've had to use offline mode right off the bat, but in the few cases where I've had no internet from a cold boot, I've been able to use it just fine.