This is why I think there was no DNA, or it was somehow corrupted.
They really didn't need to ask all men of Delphi for DNA (remember, they didn't know "how local" he was). But let's say, they had DNA. And RA is a local from Mexico, Miami county. I don't know his ancestry, but he looks like a regular NW European. Even if only one parent is from this ethnicity, the Parabon might have had their job cut for them, as descendants of NW Europeans are the most studied ethnic group in the US. Given how many third cousins live around, there should have been some DNA in Gedmatch.
So i don't think he left a lot. Other options: BG left DNA, but processed it somehow so there was nothing to collect. Possible.
Even more likely, the CS represented a DNA mix. And the locals have similar DNA; if they haven't moved out of IN for two centuries, they might be a somewhat closed group. Separating mixed DNAs, essentially, from one village, is hard, and the technology was just developing in 2017. It is better now.
If there was a special DNA (left where it should not be expected), it would mean a lot, but then, the bodies staying overnight and elements might have played the role in making it "a bad sample".
Old cases are being solved because twenty years ago, the perpetrators didn't know about DNA potential, and were uncautious. Now they know, too. Now we won't be finding that much DNA.
JMO, in Delphi case, it could be a long time of painstakingly separating DNAs in a mixed sample, comparing them, separating again... it could take a lot of time.