There are differences between under-developed and under-roasted.

Plenty of info available in google.

If you still remain unsure or confused, best advice is to book yourself onto a sensory training class......a penny or 2 will drop.

What do you taste ?........ that is the only criteria....don't look at graphs, charts, logs, curves, times, temperatures until you have formed a solid opinion on what you have tasted, then you work backwards by playing detectives, putting the puzzle together by investigating how it came to be.

The modern coffee landscape experiences a greater proportion of under-developed roasts compared to under-roasted and hence people often confuse the terms or are even clueless as to the differences.

Under-development is a roasting defect often achieved without choice.
Under-roasting is a deliberate choice.

The key point is that deciding if a coffee was technically under-roasted is often debatable......one person's opinion as to whether it was the right roast level WILL differ from the next. It comes down to interpretation and intent of the nut behind the wheel when the green stuff turned brown. Any position or decision can be explained or defended when the whole story is understood.

After all, style is a personal thing.

Thanks for the comments and words of wisdom on distinction. Good ole "intent" hey.

Tastes I'm getting are a caramel nutty sweetness from a PNG/Kenya/Columbia blend that's rocking my world at the moment, not sure I'm tasting anything vegetal but I haven't really trained my fairly uneducated palate to distinguish grassy/vegetal flavours. Not to say what I'm tasting isn't under-developed (it probably is to a slightly more educated palate than mine). I'm getting the most amazing caramel aroma off the grinder. Certainly the most aromatic blend I've ever played with.

Speaking of aroma, Does aroma have any part to play whatsoever in determining under-toasted coffees? Can you smell vegetal/grassiness either while bean  or off the grind as a precursor which manifests itself into the cup?