You can look at the adipose fin and tail colors, humeral and body shape. At that size it's pretty clear. But it's when they are juvies (1-3") is when it's very difficult. Last year I spotted quite a few tats being passed of and sold as armatus. Others will surely chime in and give you the confidence you need, since you've already been told what it is. I have both armatus and tats available for sale right now, but I won't ship to NL, unless you ship me back something in return (joking of course).