All bets are off with SAR, it's no good expecting something like 25C to be similar to 2C-C with a reasonably big difference like the n-benzyl group, which can force the orientation in 5-HT2A to be quite different. The astonishing thing is that despite certain similarities in structure between say PEAs and tryptamines, I think some actually seem to bind flipped in orientation compared to others.
Not sure how much similarity in orientation there is between lysergamides and NBX PEAs. Also I wonder if any similarities like between the 4-chloro PEAs come from activity at receptors other than 5-HT2A where the activity is less altered.
NDTDI type stuff, RU-28306 or the NDEPAs are different in that they are constrained or simplified versions of existing drugs, mainly the lysergamides or a bit the tryptamines. Varying alkyl sizes, attaching a group that changes a lot of properties or simplifying / constraining a structure can all have results that I think often can't be compared, the approaches as to why making the modifications are expected to increase binding / activity are not the same.
I think indoles react with Ehrlich's unless the reaction that apparently makes some colored conjugated not-quite-symmetrical dimer-ish compounds is obscured. Delay of reaction with 1-acyls might be a sign of that? Usually indoles or lysergamides are not hindered on that side though. Maybe you also wouldn't get a color reaction if there are changes made internally in the indole nucleus that would prevent conjugated species to form? Unfortunately I forgot how similar or not such compounds are to something like indigo, it was really not easy to find info on Ehrlich's complexes.
What does "it looks similar to NDTDI to them" mean? How did they look at it?
Seems like there is a lot of mystery and suspicious surrounding these few compounds, but some of the suspicions are impossible. Speculation can be interesting but pure guesswork or suspicion about the ID seems pointless. It's best just waiting on analysis.