Lol, I don't have any evidence as the fish have been dead over 10 years. However, I'm 100% certain they both laid eggs. I got them young, body size about the same as a quarter. I wasn't even a teenager yet, and I originally bought 3. The two that lived 10 years were oddly colored (one siamese-colored and the other like a tortoise shell cat) so there's no mistaking them for another fish. They killed the 3rd within 2 weeks, so I added another. They killed that one too, so I assumed I had a male & female pair (even though they were tiny). They quickly grew into adults and I noticed the siamese laying eggs on the left wall of the tank. I watched her lay them one by one. Then I saw the tortoise shell laying eggs on the filter intake. Again, watched her lay them one by one. I saw them both lay eggs several times over a few years. Of course, the eggs always turned white and were either eaten or cleaned out by me. I tried adding a male to the tank twice, but both times they killed the male. After awhile, the siamese stopped laying eggs, but the tortoise shell continued to. The siamese never changed outward appearance as far as I can recall, but she was always a bit bigger. Then, one day I saw her “shimmying” over some of the tortoise shells eggs. Didn't really think much of it at first. Then after a few sets of eggs, they stopped turning white and I ended up with fry. They had a few batches of fry, but always ate them. I figured it was because they were in a small tank (can't remember if it was only a 10g or a 20g, but both are small for such large angels).
The whole process took at least a year, maybe even 2. Personally, I never would've believed it of I didn't see it myself. So I don't blame you if you don't! Lol but what purpose does it serve for me to lie? And even though I was young, it was something I witnessed for years. I got them at the age of 8 or 9 and they didn't die until I was 19. It took until they were around 6 for the siamese to “switch,” which would mean I was around 14 or 15 at the time.
I've heard of this happening with livebearers, but have only heard of it with angelfish one other time...and I don't know if I believe him. He breeds them and has for several decades, but I still think he may have just mixed the one up somehow...
Not sure why it happened with mine when it wasn't necessary. Maybe the siamese was born a hermaphrodite or had some other birth defect. I'll never know. :/
) Hopefully, if it happens again to someone, they will document it properly. It would definitely be an important find. 
