Are They or Aren't They?

These are my 6 Black Australorp chickens. The end result of $50 worth of fertile eggs. 6 from 24. The start of my flock.

BUT... 2 of them are different and I have been told by 2 different people that they are not Australorps but Plymouth Rock chickens.

I was thinking that they might be roosters and so were taking longer to blacken up but now I'm starting to wonder. They all looked the same as newborns, they all had white on them. These 2 even have different coloured legs.

So, 2 look like the one on the left and the other 4 are black like the one on the right. What do you think? Different breed?

I have emailed the lady that I bought the eggs from but don't know when I will hear from her.