A Weakness of Migration Analysis to Evaluate Credit Concentration Risk

A weakness of migration analysis to evaluate credit concentration risk is that the

A) information obtained for this analysis is usually ex-post (i.e.after the fact) .
B) information obtained for this analysis is ex-ante (i.e.before the fact) .
C) analysis makes use of historical data classified only by industries.
D) analysis makes use of historical data classified by individual firms.
E) migration of firms may only be temporary.