I had some of these same questions and concerns last year (and maybe the year before), but never really got clear answers on how everything works. Maybe having the questions in one spot to be discussed and cleared up would be helpful.
1. Has it always been that you need to log in during the anniversary in order to be eligible for the gift that year to "count"?
I made my account back at the start of 2008, so I am only on 12 years af far as the anniversary is concerned. I think there have been years, however, when I was either not actively playing or too busy to log in for the anniversary event. So if logging in during the event was needed for it to count, I should not be getting year 12 now, but I am. Did this change in the past few years?
2. What is the anniversary gift period that runs from 4/23/2020 until 4/1/2021 for?
This was listed for last year's gift as well and ran until 4/1/2020. I asked last year if that meant all of your characters needed to log in and get the gift before the following anniversary and never received clarification on it. Testing now, though, a new character I made 10 minutes ago received gift boxes from year 1 all the way to year 12, so I did not have to log in before April 1 to get last year's.
3. Will new characters receive the account-wide Anniversary Celebration Pig even after the anniversary period?
I have logged in a few of my characters to get the Anniversary Celebration Pig skill, but do I need to log ALL of them in to get it now? If I log one in after the anniversary or create a new character after, will the skill still be granted since it is account-wide?