Allowing, of course, for the fact that the formulas used aren’t exact, I think they are based on Jerusalem time.
I suspect it would not be too difficult to calculate when there is a full moon occurring that soon after the vernal equinox on a Saturday/Sunday depending where you are in the world. The Pope could just do what he originally did and set the date for Easter based on that.
Here are the full moons until AD 4000
And here you can find the equinox until the year AD 3000
You’ll note those are for Universal time (what we used to call Greenwich time). You’d have to decide what location to use for your calculation. As I suggested (and was suggested before), Jerusalem time seems like the logical choice.
My point is in how many years would such an alignment occur as to cause a problem. And now that I think about it the Vernal Equinox & Full Moon is not an issue unless they both occur simultaneously. Then the only issue is if the full moon occurs when it is a Sunday with some time zones still in Saturday or on a Sunday with time zones already in Monday. And that can be solved without resorting to Jerusalem time by the Pope decreeing if it is a Saturday/Sunday combo then that Sunday is Easter and if a Sunday/Monday combo then the next Sunday is Easter.
That would work for the Catholics. I’m not sure how Protestants and Eastern Orthodox would feel about this.
But it’s better that way! More treats because it’s two different days instead of one where the Easter Bunny conspirers with your parents to give you less overall. In this case, the whole is LESSER than the sum of the two parts.
Why are some dates, e.g. April 20, not on that chart?
I believe the actual medical term is Equinox Simplex. I think it’s related to Herpes Simplex 
They are on the chart; the issue is that whoever created that chart formatted it in such a way that the labels along the bottom (x-axis) only label every other bar (date). There’s a bar for April 20, for example, just not a label that says “April 20” below it.
Now I’m humming P.D.Q. Bach’s Chorale Prelude on an American Hymn for the Last Sunday Before the Fourth Day of the Seventh Month After New Year’s Eve.
Easter was on my birthday (March 28) the year before I was born. My team, the Cleveland Indians/Guardians last won the World Series that year as well. Neither has happened since.
However, Easter will be on my birthday again in 2027. I hope I get a 2-fer. If not maybe I’ll make it to 2032 which is the next year Easter falls on my birthday. 2100 is much to far away to wait for.
My mother was born on Easter Sunday, and her birthday was never again on Easter during her lifetime. My sister’s birthday was two days later and has been on Easter three times.
Your sister was born two days after your mother? Was she a tribble?
My sister’s date of birth was two days after our mother’s, but 26 years later.