(By particular I mean individual in the sense that it is unique.)

Also, if something is a replica of something else, it must be wholly similar to that something else. To say X = Y with the condition that X need to be +Q is not the condition of X = Y as you claim - rather it is the condition of X + Q = Y.

The first point stresses that since each individual thing is unique, any similarities found between two things must come from something outside those two things - presumably our mind. An example of this could be where an ancient astronomer discovers two very distant stars, both of which appear exactly the same to him. Both these stars must have different histories and compisitions, but still, they appear to be merely two dots of light to him and exactly the same to the point where they are different by number alone.