Roll Rate versus Rating Migration Matrices

Roll matrices (based on Roll Rates and rating migration matrices are related in various ways:

Both utilize the machine of Markov Chains and Transition Matrix mathematical concepts
May share some states and corresponding migration rates
Delinquency profiles may be inputs to rating models

But there are also significant differences:

a roll rate matrix is based on observable states with few if any Model Assumptions, whereas an internal or external rating involves the use of additional data and interpretations that may introduce significant subjectivity and Model Risk (but also - in principle - allow more forward looking risk assessment)
the states of a Credit Rating System will typically introduce finer resolution to the Current state of a Roll Rate system on the other hand the credit rating system may have lower resolution around delinquent states