As stated, out of the common TSNs we get in the states (99% fasciatum, 0.5% tigrinum, 0.5% reticulatum, ~0% everything else), only by 1.5'-2' mark are we usually able to make a guess at their species.
All juvies look exceedingly similar, all have the white lateral stripe.
The coloration pattern undergoes a heavy evolution with age / size... plus variability (geographic for w/c, possible hybridization for farmed TSN) and taxonomic uncertainties do not help.