Church of Light literature says the Prenatal Epoch method of rectification is about 70% accurate IF the birth time is known within 30 minutes or so. I've used it in a few cases to adjust/rectify some known times (including my own) and it has appeared to give good results.
If the birth time is completely unknown, I'd say it would be necessary to use other techniques to get the birth time closer, then apply the Prenatal Epoch. Secondary (aka Major) progressions may enable you to get the progressed Moon within a degree plus or minus, and then Minor progressions of the Moon to tighten that up. I've used that a few times with credible results.
Secondary progressions in this application would definitely need to be Bija corrected (ie use the Sidereal, not the Solar, day). To put it another way, use 24 hours of Sidereal Time, not 24 hours of clock time, as the definition of a day in the "day for a year" calculation.
One resource to review for the general concept might be the Zipporah Dobyns book Progressions, Directions and Rectification. For general guidance on progressions, C. C. Zain (Elbert Benjamine) Natal Astrology: Part 2, Progressing the Horoscope. In the Primer of Sidereal Astrology by Cyril Fagan and R. C. Firebrace the concept of Bija correction is put forward, but because of the way it's calculated, it's not at all intuitive what exactly they're doing IMO.
