Unique is a singularity: where nothing can ever be the same.
There is no such thing as totally unique, or almost unique. There can be no qualifier for this adjective. It is either unique… or it isn’t.
It must be silly to think that a snowflake could be unique. How could every one be different? There must be a zillion snowflakes fall every year – surely they must repeat at some point.
Let us assume we are talking about the snowflakes we are accustomed to – fuzzy bunches of molecules, like this for example:
Even at this scale, you can see the symmetry is not exact; some parts of the crystal are different on each arm.