Before revision:  At the extremely simple end would be chain-ladder-compatible data, and so the alternative data structures available enable proposed loss reserving models to be tested against more challenging data sets. Indeed, the user may generate a collection of data sets that provide a spectrum of complexity, and the collection may be used to present a model under test with a steadily increasing challenge.
After revision:  The user may generate a collection of data sets that provide a spectrum of complexity, and the collection may be used to present a model under test with a steadily increasing challenge.