As emails are wont to be, some won't be delivered accurately due to spelling errors, new emails but forgetting to notify, or lost somewhere on the huge web of data of this world. Thus, those who desire Legacy and feel that they should have it, but don't know where to confirm this due to lack of email, are being lost about how to identify themselves as such.
Please note that all material shown is property of Square Enix, and may be taken down with their prompts and at their discretion. My character and account name have been masked/censored, and my character himself may not appear due to his tendencies to strip while in his inn bed.
Checks in order of priority:
1. Square Enix Management Account page
Log into your Square Enix management account.
Under Services and Options, please click "Select Service"
Once you have done so, please select "FINAL FANTASY XIV" or press the corresponding image.
If you are eligible for Legacy, you should have the legacy icon near the right of your service account(s). Please note that beta accounts DO NOT acquire Legacy status.
2. Character Loading Screen After Login
Proceed as normal in opening up game by using the boot program. Start playing, and navigate towards your character selection screen. Select the Service Account you wish to play on. If you are eligible for Legacy, the Legacy icon should appear on the very top left.
3. Email Sent from Square Enix Regarding Legacy
Open up the email box you use to collect usual emails from, or the one you have inputted into your Square Enix account. If you are eligible for Legacy, you should see an email from SQUARE ENIX, titled "An Important Notice Regarding the FINAL FANTASY XIV Legacy Campaign". Click on it to show the following page if you are eligible:
That ends the current checks that I am aware of for legacy. If there are more, please let me know so I may endeavour to help out others.
If you have all three checks, that is excellent - it means no doubts about your status as Legacy can be raised. Suffice to say, that if you have acquired at least ONE of the checks, then you are eligible for legacy anyway. However, foremost should be your Square Enix management homepage followed my your in-game character screen.
May the Twelve be with you!