Note that those dates are somewhat oversimplifying things. For example, in Sweden there was something called "same-sex partnerships" from 1995 which legally was equivalent to marriage.
It was equivalent to marriage in Sweden which is an important difference, civil partnerships are inconsistent[0] and not necessarily transferrable across borders.
You're right that just listing the dates for same-sex marriage doesn't tell the whole picture, but adding civil partnerships and their details would necessarily expand the comment to something closer to a book.
[0] for instance in France civil unions are quite literally a marriage lite, open to all and very commonly used as a legally recognised engagement by heterosexual couples (>90% of civil unions are heterosexual)
