  Some of the main results of [Cotti G., Dubrovin B., Guzzetti D., Duke Math.
J., to appear, arXiv:1706.04808], concerning non-generic isomonodromy
deformations of a certain linear differential system with irregular singularity
and coalescing eigenvalues, are reviewed from the point of view of Pfaffian
systems, making a distinction between weak and strong isomonodromic
deformations. Such distinction has a counterpart in the case of Fuchsian
systems, which is well known as Schlesinger and non-Schlesinger deformations,
reviewed in Appendix A.
