My rough and ready guide would be as follows.
Any figures in harness with plate gorgets are pretty much restricted to c.1400 onwards. Tall and pointed great bassinets can be stretched a bit further back, but no really beyond c.1390, with pointed visors turning up around a decade earlier. However, full great bascinets themselves go back to c.1350
Faulds (overlapping horizontal bands of plate worn as skirts) appeared c.1370 with brigandines appearing about the same time.
Besegaws, the circular plate at elbow, knee, and shoulder joints, appeared c.1360 with fans appearing about a decade later.
In short, I'd agree that Nicopolis sits pretty close to left of arc for the range overall with the odd figure being useful earlier.