Is there an easy DIY way to, say, compare two vials of L to see if they are different source crystals? Beyond subjectively comparing the experiences.

The fact that it is L isn't in question, but whether or not it's different source is.

Thanks in advance

If all you want is to establish if they are the same xtal or not, I would evaporate some of each vial and compare the residual visually. Not a full proof method but it might work.

I know that Energy Control test for the amount of iso-LSD which can be left over from the synthesis, although LSD can degrade to iso-LSD so it would depend on both samples having not degraded before testing. I read that for EC to test for purity they need at least 10mg of the crystal so I don't think there's an easy inexpensive way to test it conclusively, unless perhaps your name is benzyme.

I might just try this, can you see differences with the naked eye or would you recommend magnifying?

The issue is that lsd dose is measured in micrograms, so unless you evaporate a big portion of your vial you are going to end up with a minuscule amount of residue. Magnification will be required I believe. And as I said before, this is far from being a reliable test.
What swarupa said will be a better option but its not diy...
And lastly, consuming it in order to tell the difference in experience is also problematic since your vials are probably not dosed exactly the same.

Yea the vials in question are very likely not dosed even closely the same. There's suspicion that 2 was made into 3, so the person would like to know if they are truly different or just the same split up. I'll look into testing as swarupa suggested; they have nothing but time and money so I don't think they'd mind lol.

Thanks a lot for your input, and happy trails