Been thinking about these two things lately and their connection with Ex Miscellania.
It seems like Ex Misc is simply a collection of various lineages similar to those discussed in Mysteries 4th, and in various places in the 5th ed. books like ROP:D, ROP:I, HOH:MC and Mysteries 5th ed. Could most ex misc be simply various small lineages of exoteric mysteries just flung together? If that's true could the mystery initiation rules be used to teach access to the various secrets of their lineages or alternatively, if the ex misc lineage want to spread its knowledge, would the teaching supernatural virtue be appropriate. In ROP:D, its possible for a Mythic Companion (or mage for that matter is suppose) to learn another power or method outside of its tradition in a way similar to that outlined in Mysteries. Of course Giant Blood, Mythic Blood and Faerie Blood aren't "learned" but other supernatural virtues can be learned and flaws can be imposed through sacrifices/ordeals. However, why couldn't a magus be inducted into the mysteries of ex misc Gurgurach with the proper teacher?
One of my players is Ex Miscellae of the Lineage of Maria from the 4th ed Mysteries book. Virtues and flaws of the line include Holy magic, craft amulet, sense holiness, vulgar alchemy along with piety and nonviolence flaws. We are currently working on how she will advance into greater alchemetical skills that are similar to the various alchemy progessions of The Mysteries.