If the Hansens as Xenobiologists could do it, so could other people or organisations. There is also the possibility of Borg encounters along the edge of Romulan space in the 2360’s, Romulan bases were destroyed by the Borg in this decade and the Federation was blamed at first. The El-Aurian species could also have had genetic data from the Borg after their encounter with the Collective in the 23rd century.I've read the suggestions you put in place, but I also countered them with the fact that the protege's of Soong simply wouldn't have the means and probably the motivation to go around the galaxy.
Stumbling upon TW conduits (unless you know what you're looking for - like the Hansens) would be downright nigh impossible prior to 2366 unless you knew what you were looking for (let alone opening them) ... and even for the Hansens (who were actively searching for the Borg) it was difficult to find a cube (and go through a TW conduit while following it)... not to mention extremely dangerous.
A Borg cube containing assimilated members of these Delta Quadrant species could come to the Alpha or Beta Quadrant saving any geneticist from having to travel to the Delta Quadrant in person. Borg only assimilate to enhance their biological perfection so they would have chosen quality species to become drones, including those mentioned as being a part of Dal’s genetics. Why can you not envision this idea @Deks ? Or potentially a Caretaker like entity could have brought members of different species together, maybe even the Nacene themselves? Suspiria for example would not have been the last of her kind at the time of Dal’s creation.Also, I just don't see the protege's of Soong being able to get their hands on Vidiian, Krenim and other DQ species DNA.
The Vidians would have hunted protege's of Soong for their body parts (and were similarly advanced as the UFP and more advanced in medical science).
Krenim DNA... even VOY couldn't get its hands on a DNA sample from the Krenim. Perhaps in the original timeline when they were on friendly terms with the Zhaal... but not after the temporal reset (which involved a few lines of polite exhange over a viewscreen).
I doubt the Protege's of Soong would have been able to reach and roam the DQ in the first half to mid 24th century looking for DNA samples.
But how do we know that there was not a species 8472 encounter off screen in the milky way previous to 2374? Someone could potentially have even travelled to fluidic space. Any blanks are not ‘facts’ until a writer/producer decides otherwise.Plus, I already mentioned the fact that species 8472 wasn't even in the Milky Way galaxy before 2374 (and they only 'visited' briefly to fight the Borg).
The Nacene could have transported an 8472 bio ship in to our galaxy at an earlier date. A bio ship could even have fallen through a random anomaly in to our realm at *any* point in the 24th century.
What about all of the other Founders sent out to explore the galaxy? You did not reply to this suggestion of mine. DNA could have come from one of those 100 - it was not just Odo that was sent out as an infant.And as for acquiring Dominion DNA... depends from which species (there are multiple species as part of the Dominion seeing it’s a political organisation and not a species name).
Odo's sample may have been smuggled off world by Dr. Moira, but I suspect the Cardassians would have prevented something like this as they would want to keep any and all potential advantages to themselves.
Perhaps. But why *only* UFP genetics? A geneticist would have been acting illegally, so would not have been bound to only use United Federation of Planet members DNA. A geneticists would have picked the best traits for the hybrid regardless of their species political alignment which is irrelevant. They need to keep a closer eye on the animation team in the future or make sure that they are coordinating with the writers, or vice versa. There was also a potential mix up with the Enterprise E appearing in the finale. I would like to think that this was not a mixup though.It makes a LOT more sense that Dal was created in 2366 as a result of mixing DNA of 26 known UFP member species. The DNA samples are readily available, and the protege's of Soong could get as many as they wished and then defected from the UFP to conduct genetic experiments in seclusion resulting in Dal's creation (because otherwise, you enter into a convoluted galactic search for samples of unknown origin and species that no one - including even Protege's of Soong could have known existed prior to this time frame - and if they were scientists, they likely wouldn't be chasing unconfirmed tales of some unknown species residing thousands of LY's away... they'd work with that they already had - and UFP already had a HUGE amount of varied species who possess unique atributes to work with).

It is also assumed that the Soong protégé was acting alone. This character could have been acting on behalf of an organisation - a hired hand to do the genetics after someone else collected the samples from around the galaxy.
There are too many unanswered questions and all that we can do is speculate until the writers show us something solid.