Ultimate Authority
Ultimately, the decision on appropriateness when writing CCC adventures is determined by the DDAL administration. Each Convention Created Content module must be submitted to them for approval before it can be played. Groups and individuals with a long track record of producing quality content are given more leeway.
Established Patterns
It works out very simply...
- Tier 1 = Uncommon
- Tier 2 = Rare
- Tier 3 = Very Rare
- Tier 4 = Legendary, but not all that often.
A variety of common magic items are a fairly recent occurence. To my knowledge, they have not been explicitly included in anything except DDIA-XGE: Underworld Speculation, the introductory module for Xanathar's Guide to Everything where they first appeared.
How many? One
As for how many magic items: one, always one - regardless of length. Hour-long introduction modules have none, and Epics sometimes have more, but neither are part of the CCC program.
I can speak from personal experience with the CCC program. I am indirectly affiliated with a CCC writing group; they submitted a module for a convention I staff for. It had two magic item rewards, both very thematic. They were told to pick one or the other by the DDAL administration.
A Note on Precision of Language
The question says...
the process for submitting adventures from conventions to Adventurers League to become certified “legal” CCC-AL adventures.
...but it's not an accurate statement.
CCC adventures are sponsored by and affiliated with a convention they premiere at, but the creation process starts long before the convention takes place. They're not created freely by the conventions to "become certified" later. They are authorized by the DDAL administration to premier at a particular convention before writing even truly begins.
I would say no.
The rule text specifically states "...allows a night hag to become ethereal" and the night hag has an action called "Etherealness", which requires a heartstone.
The stone does not provide this ability, it only enables the night hag to use her ability.
On a more balance-related note, it would be an amazingly good and game-breaking item. It's unlimited castings per day of Etherealness (a level 7 spell).
As for the cure disease effect... Looks like it would work, RAW. Not terribly game-breaking either (though most diseases would obviously become a non-issue).
Best Answer
Version 1.1 Player's Guides
The “+1 rule” is shorthand for the restriction on being able to use the Player's Handbook plus one extra source to build your characters for the Forgotten Realms campaign.
WoTC has two different campaigns that utilize different limitations (currently v1.1).
Forgotten Realms (Waterdeep/Dragon Heist)
From page 2 of the 9.2 version of the Adventurer's League Player Guide (ALPG).
Eberron (There is no +1 rule per the ALPG linked above.)
From the 1.3 version of the Eberron Campaign Player's Guide (December 2019), which accompanied the Oracle of War campaign:
The previous guidelines used for the Embers of the Last War campaign, released before the publication of ERftLW, substituted the below sources for that book and did not allow any exceptions for use of other material: