Background Information
Go use the search function you noob. HA! Just kidding. Since I really can't speak to any stories of what happened with DP employees, former employees, or licensed DP products, maybe some crude pictorial deduction will help explain was is generally known. Please pardon my photoshop work.
I'll start with the mystery breed. I've drawn arrows to show some things the helmets share on these pictures made available by Art Andrews, SgtFang, and TDH members, so let me know if any of you don't want them up. I'm using pictures of the SgtFang, MS1, "Lava," Rogue Studio's buck, and the original helmet that is often described as the "pre-production 2" helmet, or PP2. They are by no means the extent of the similarities or differences, but I'm just pointing out some glaring items. The arrows contain colors, and I've given you a key. Red is strictly a characteristic common to "Mystery" casts. Teal is a "Lava" characteristic. Green is a shared original ILM Fett helmet characteristic. Hopefully, this can show how some things are shared, or not shared, between casts. There are many other differences between both the Lava and the Mystery, but these are simply ones that I can show easily in some photos I have on-hand. This is by no means a scratch-by-scratch comparison down to the millimeter which is probably beyond the scope of this thread. The last photo is simply to add more question marks as the red arrows follow the mold line differences between the "Lava," original ILM helmet, and Rogue Studio's buck.
With the "Lava" and Mystery helmets, the commonalities are uncanny starting in the forehead arrows which are mal-aligned along the front-to-back mold line. Some of what started out as errors or rough spots in the "Lava" are manifested as solid inconsistencies in the Mystery helmets. The right mandible hex jog appears to have started in the "Lava" as a scrape/dent and smoothed into the Mystery as a jog. The left rear trim behind the ear looks like a mold flaw in the "Lava" while it is more smoothed yet flawed in the Mystery line. The cheek corners and ear trim bottom corners are of course clearly intentional modifications common to both Fang and MS1. These are elements the the "Lava" does not have. However the upper left corner of the dome squaring-off warp that shows up in the "Lava" shows throughout the Mystery helmets like a big white flag. This is significantly different from the original helmet and it appears like something that would happen in the molding or casting chain of events rather than any intentional modification. The dome is so multi-dimensional that even the best fan-sculpt has a hard time coming close to approximating such compounded curves in different directions.
*note, the SgtFang example is the first version, rather than your current offering which lends repairs to some of the areas in question.
Editorial Opinion
This evidence is why the most popular theories surrounding the "Lava" are that it is a product of either a highly degraded mold (that produced Rogue Studio's buck), or some of the sloppiest molding and casting work ever, a combination thereof, or a second horrible or degraded mold entirely. The "Lava" is interesting, but it and any members of its family are some of the sloppiest, most horribly warped tubs of lard I've seen in Fett. The fact that they contain direct elements of the original helmet can't really make up for the fact that the dimensional departures from the original cast are so severe that it would take so much work to repair accurately that it would lose too much of its progenitor only to become another fan-made cast. They are more interesting left alone rather than painted, yet I would also add that the "Lava's" warping on all facets has either been repaired or is not present in the Mystery line other than the dome. On the fringe of this discussion is the popular BobaMaker helmet which, due to its uncanny similarities to a Mystery cast, I deem as a modified Mystery recast until I see a photo that shows otherwise. As for the scratched-up dome of the original helmet, word on the street has it that the de-mold process didn't go so well and the mold was cut along that line with sharp tools. This gives credence to either creating another mold, or attempting to repair or use a highly damaged mold in a different way, giving birth to the "Lava."
SgtFang, I can believe that your original helmet was in rough shape, but the reason why I don't think you actually had a "Lava" to start with is the fact that the common Mystery elements are shared exactly and independently between your helmet and the Marrow Sun. Right off the bat, the two casts were showing identical modifications made by someone other than you, somewhere, outside of the 1st and 2nd generations of the original. Unless you had knowledge that one of your helmets is a recast of the other after reaching either of your hands, the MS was known to have originated in a separate eBay auction around the same time as yours did. If you had any more photos of your original helmet as you received it, that could help solve the mystery.