Reviewed the Lost Mine adventure over the weekend -- it does say that it's an adventure "for 1st level characters" and "[d]uring the course of the adventure, the characters will advance to 5th level."
Should also be noted that the intro to Part 4 (Wave Echo Cave) says, "This part of the adventure is designed for level 4 characters and assumes that each character has earned at least 2,700XP. If the adventurers skipped too many of the optional investigations and encounters in part 3, they might not be 4th level, and many of the encounters in this section might be difficult for them." It's the only part of the adventure (other than the very start) that mentions a specific character level. I assume this is not a restriction on AL characters that can play this section of Lost Mine, but it was curious to see.
In each of the first three iterations of the ALPG, there was a sidebar on Lost Mine as an 'evergreen adventure'; each noted the "from 1st to 5th level" description similar to that contained in the adventure itself -- none specifically listed the adventure as 'tier 1'. The sidebar was apparently removed for the Season 4 ALPG and has not returned; the Season 7 FAQ does mention Lost Mine under Event Organizer Questions, but does not note a level range or tier.
Given that Lost Mine is treated more like a hardcover than a DDAL/EX/etc. adventure, and that mixed-tier parties are explicitly allowed (though not required*) in hardcover adventures (FAQ 7.1, pp.12-13**), a clarifying note expressing the official AL level range for Lost Mine might be worth adding.
* - "DMs may choose to avoid mixing tiers in order to maximize ease of play -- restricting play to that [of] a specific tier within the adventure's level range."
** - "Unless the adventure specifically says otherwise, characters of different tiers can adventure together providing each character's level falls within the adventure[']s listed level range."
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Pauper