Perhaps anyone reading my "literature review" has come up with the same questions I have. For example, there seems to be an assumption in all of the books I've read except Devlin's, that past lives were rather homogenous in their problems and needs for development. Further, much of astrology, notably horary, is theoretically testable. If I predict that you will have many children, are an introvert by nature, or that your lost keys are under the bed, you can report back on your family size, your results on the I-E scale of the Meyer-Briggs personality test, or whether the keys were under bed or not. In contrast, we have to take past-lives/karmic astrology on faith.
But just to wrap up with the books on my shelf.
Jan Spiller, Astrology for the Soul, also relies heavily on the nodal axis. Unfortunately she conflates sign and house number. The NN in Aries or in the first house has the same meaning for her, leading to confusion for, say, people with the NN in Aries in the 7th house. Spiller's NN Aries people are apparently coming off of past lives as "housewives, secretaries, counselors, and assistants." (p. 22) Their past lives had remarkable similarity in primarily being a support person for somebody else. This is one book untroubled by demographic realities of the past. For example, NN in Gemini people had past lives as wandering holy men, nomads, and hermits. They have had many incarnations as "Philosopher Kings." (p. 113)
Since roughly 1/12 of the world population today will have the NN in Gemini, demographically there just were not sufficient numbers of philosopher kings in the past to accommodate all of them. Spiller's delineations seem to be entirely intuited or imagined.
Stephen Arroyo, in Astrology, Karma, and Transformation, views karma as intrinsic to reincarnation in an "eye for an eye" or "tit for tat" model derived more closely from Hinduism. Saturn is the "lord of karma" and squares and oppositions indicate past life issues to be worked on in this life, but people have the ability to improve their situations through pro-active uses of their horoscopes. The element of a stressed planet indicates excesses according to the element's nature that need to be disciplined. Virgo, Pisces, and Scorpio are karmic signs, as well as the 4th, 8th, and 12th karmic houses, because they symbolize shifts in human consciousness. Arroyo is not specifically interested in who you might have been in a past life. Rather, he has some generic delineations of this-life personal difficulties with suggestions on how to move forward.
Finally, Jeff Green views reincarnation through the lens of Pluto, which he equates to the soul. He takes past lives for granted, and views the SN as indicative of past-life residues in Pluto: The Evolutionary Journey of the Soul. If you want a modern "evolutionary astrology" take on karmic relationships, Green's Pluto: The Soul's Evolution Through Relationships, vol. 2, may be your book. Just don't ask for a particle of evidence in this book on synastry from a past life perspective.
Obviously the above list is not exhaustive. A Vedic astrologer would have a different take on past lives. I just hope to show that the topic is more complicated than merely a SN/NN delineation, and that different past-lives or evolutionary astrologers don't all agree on how to read a current birth chart for past lives; or even, whether it would be the right chart to read.