Hello Francois,
I can understand your confusion, it's sometimes difficult to differentiate on pictures these two species groups.
There are small differences with respect to eye position (rather low in
elegans group) and snout morphology (pointing more towards the front instead of down), these small differences are difficult to describe and sometimes even more difficult to see in the pictures.
One more criterion which does not always help but is very easy to see is the dorsal fin and body pattern.
As per my knowledge there is no member of the
aeneus group with a (dark) fin pattern, the fins are only more or less uniformly coloured with the colour eventually fading in some direction whereas in the
elegans group you can often find - mostly in males and in the dorsal fin - some dark stripes or similar pattern.
Likewise in the
aeneus group you will only find big blotches, stripes and eventuall a fluorescent stripe but never any small (well defined) spots, thin dark lines or reticulated pattern.
The problem is that there are also members of the
elegans group which have a pattern that would be typical for
aeneus group (possibly due to mimikry).
As you already mentioned CW097 (and CW097) are from the wrong region.
Patternwise CW019 is very similar, a member of the
elegans group with a pattern you could also find in the
aeneus group...
From what I can see in the pictures your corys belong to the
aeneus group, CW026 is a member of from Venezuela which looks also somehow similar but I think that you have a variant of
Corydoras aeneus from Colombia without any C or CW number and which is possibly sympatric with CW019.
Cheers,
