I've also heard that popping only works within a few hours of birth?
Don't quote me there, it could be a bit longer, but I'm fairly certain there is a limit to how long you can use that method.
And probing does sound risky..........not sure what to tell you, Tina.
I can tell what most of my babies are by the tails, even though they're tiny. The differences still seem to be there. Again, I could be completely off in that judgement too, but it worked for Deejay when she was a baby!