Young SAE or FSAE w/ black to tail?

I've been to this site http://www.aquatic-gardeners.org/cyprinid.html
in an attempt to distinguish between the SAE and FSAE. I had a SAE for
about 5 years and he or she just died. I went to my LFS and they had
three, what they were advertising as, SAE. They are very small and I
noticed that the black stripe does not go to the fork of the tail. I
believe that they may be FSAE. I got them anyway.

I was wondering if the stripe goes to the tail from birth(hatching) or
does it get there with a little bit of age?

I'm color blind so the yellow fins doesn't do me any good. The black
stripe to the fork of the tail is what I rely on, without black on the
other fins.

Any guidance would be appreciated.

John