If you're storing the timezone (and by that I assume you're doing so unambiguously, because offset alone doesn't tell you hemisphere/DST rules, and timezone nam

If you're storing the timezone (and by that I assume you're doing so unambiguously, because offset alone doesn't tell you hemisphere/DST rules, and timezone names are not unique), then you're effectively using UTC, albeit storing it in a non-normalized format. The flaw in your logic is in assumption that "intended time" is always fixed relative to one user's clock time. For international events, intended time is physical time. If it's a friday and I verbally arrange a meeting with someone in Sao Paulo at 3pm BST the following monday and that translates to 11am PST today for me at San Francisco, but if there's a DST change for me over the weekend, the intended time is still 3pm BST, not 11am PST, because in such cases, the general logical expectation is that whoever is getting a time change is the one who should be on top of it. In either case, you'd be able to recover "intended time" (for any meaning of the term) 99.9999% of the time regardless of whether you used UTC or local time+timezone. If there was indeed an unlikely event of an unannounced DST policy change, then whether intended time is wrong depends on who's affected. If it's an international meeting and intended time means physical time, then local time+timezone does not capture true intended time. Likewise, if intended time means local time for a single user, UTC will be the wrong one. But as I said, this case is vanishingly unlikely. A lot of code doesn't handle integer overflows correctly because they are unlikely too and the world is still humming along just fine.