"Synchronicity is the experience of two or more events that are apparently causally unrelated occurring together in a meaningful manner." (Thank you, Wikipedia.) It's a Jungian thing, and more than mere coincidence.
There is also a name for inventions, ideas, etc. all popping into existence close-to-the-same time in different places (and by people who haven't been in contact with one another). And no, I don't remember the term for it (but it may well wake me up in the middle of the night).
This type of thing happens with songs - with any creative effort, really.
I was at a friend's hone studio yesterday, listening to some recorded tracks. One song in particular jumped out at me (heck, they were ALL good!) - very moving, beautifully performed.
It also happened to be on a topic that had been nudging my brain lately.
Now, this might not be so surprising if it were a timely topic, like something going on in the world, the environment, in politics. But it wasn't. In fact, it was 260-year old news. Whoa!!
Once, I would have thought "dang...someone else wrote it already. Oh well" and shelved the idea. But consider this: What are the odds that 2 people who know each other have song inspirations about topics that are so similar -- but so far removed from present day reality?
Sounds synchronistic to me. Now, I just keep writing.
If an idea is powerful enough to make several people sit up and get inspired, well.... it's powerful.
Keep writing. Say what you have to say. The song will have its own way, no matter what!