I have watched the anime Ano Hi Mita Hana no Namae wo Bokutachi wa Mada Shiranai. It has the ED song
"secret base ~Kimi ga Kureta Mono~ (10 years after ver.) (secret base 〜君がくれたもの〜（10 years after Ver.）)" by Meiko Honma (Ai Kayano), Naruko Anjou (Haruka Tomatsu), Chiriko Tsurumi (Saori Hayami)
A few years later after I watched AnoHana, I watched an old anime, Kyou no 5 no 2. I heard one of its ED songs, and it's really similar to AnoHana's ED song. The title of Kyou no 5 no 2's ED song was like:
"secret base ~Kimi ga Kureta Mono~ 「secret base ～君がくれたもの～」" by Friends: Yuu Kobayashi, Asami Shimoda, MAKO, Satomi Akesaka, Youko Honda, Kana Asumi
So my question: Is it possible/rare for a song that is used in the OP/ED of an anime to be used also in the OP/ED of a different anime?
Has this ever happened to other anime? Or is it just a coincidence?