Avraham Avinu and Sarah Imeinu's 3800th Wedding Anniversary
Avraham Avinu was born in the year 1948 from Creation. Sarah Imeinu was born in the year 1958 from Creation. According to Midrash1, Avraham married Sarah when he was 25 and she was 15. That means that it was the year 1973 from Creation. That was 3800 years ago - or 200 19-year cycles ago.
The exact date of their wedding is unknown, however. (Could it have been Lag Ba'omer? Who knows?)
For the couple who made Aliya on their 50th Golden anniversary and had their first child on their 75th Diamond anniversary, may Hashem remember their deeds for the merit of Kelal Yisrael on their 3800th.
1 Yalkut Shimoni 78 (see the Zayit Ra'anan there), and also mentioned here and seems to be the popular opinion (but see also the 2 girsa'ot in Tanna Devei Eliyahu Rabba Chapter 18 and the Yeshu'ot Yaakov's commentary)