I just went through all 17 diamond veins you have mined. Out of those, 2 of them looked like they were very plausibly mined legitly, another 2 of them I was unsure of, and 13 of them looked like they were xrayed. I'm going to go ahead and start posting screenshots. You can see the
full album of them here, or just keep scrolling for my sort of curated display of them.
I'm basically walking down the path you mined through. I rolled back the diamonds themselves (and in some cases, sand) so I can show where they were located.
Xray #1: Dug down from a natural tunnel and then straight over to diamonds.
Xray #2: Dug down to bedrock, then over to some diamonds.
Xray #3: Dug over to diamonds again.
Xray #4: Dug over to a lava lake, which you filled in to reveal diamonds.
Xray #5: Found diamonds under lava. After tunneling to the lava.
Xray #6: Dug down to diamonds at bedrock
Xray (maybe) #7: Dug away from a tunnel, hit diamonds, hollowed the area around them out, moved on.
Xray #8: Removed some lava at bedrock, found diamonds.
Xray #9: Dug directly to another lava lake that just happened to have diamonds.
Xray #10: Diamonds under a lava lake.
Xray #11: Dug down to bedrock and found diamonds.
Xray #12: Dug from one natural cavern to another with a lava lake, found diamonds.
Xray #13: Dug down to more diamonds
Xray #14: Dug from there straight to a diamond vein that happened to be right by a lava lake.
So, it looks like you were frequently able to tell which parts of lava were hiding diamonds. You weren't just clearing out all lava to find these diamonds, because you skipped some lava pools you came across. The majority of the diamond strikes were very suspicious.