Yeah, and it's faulty. Conventional wisdom says "If the show doesn't say within the scene or before the episode ends, it is true. If the show never conveys otherwise, it is true." Every show works like that.
1. Retcon: Snow White's lie due to a retcon, not a change in conventional wisdom.
2. Flaw: The General Audience not online would believe that Lancelot was dead, becaue conventional wisdom. If Once never past season 2, 3, or 4, Lancelot would be dead via conventional wisdom.
3. N/A. Rumple isn't omniscient or omnipotent. This is breaking their own rules, which they've done numerous times.
4. Discontinuity. Not a lie, just a writer clearly forgetting.
5. Wasn't planned. (Also see number 7)
6. Only true example.
7. Vague, flowery exposition which they do with everything and each new villain that makes no sense at the end.
Not that I'm dragging the show through the muck, but there are only one notable time where it counters conventional wisdom: Robin's obliteration (which still is left open to interpretation). The rest are discontinuities (aka plot holes), retcons (bad ones being plot holes otherwise), flowery, hyperbolic exposition, or etc.
Bringing it around....If Hades said he made the UW to appear as SB, then it's true until shown otherwise. Not even the writers offer any other notion (like they did with Lancelot and Robin).