If the third column has only values between 1...15, then why did you write below cited?
And the third column has a value no greater than 20.
That's more of a rhetorical question. Though I believe, to solve puzzles, it's necessary to be accurate with details (from the beginning).
When you said you inherited this "puzzle" (obfuscated backup?), did you thoroughly check there are no further clues or documentation or other helpful details, notebooks, whatever? Any chance to find something?
At the moment I have no further ideas or inspiration what these three columns could encode. I can only ask nasty questions which may inspire you or someone else to bring up clues.
I know that you shouldn't reveal more details. Just one question: what makes you think that the first column's numbers are actually indices of the BIP39 wordlist? Sure, none of the 24 numbers exceeding 2047 may be a hint, but regarding the small sample size, it's not too strong evidence, unless there's some writing or headline pointing to it.
I don't want to bug you. My experience with people asking for help is usually, they rarely have enough overview of all the details that might help to solve or bring a case closer to a solution. Sometimes you can't reveal all, as in your case, obviously. But still, there might be more details that you don't think about that could be helpful for others to find clues.
Try to "switch chairs", did you give those who you ask here for help enough details to be able to find clues or even a solution?
Do you know anything about the person from whom you inherited? Was that person maybe a member of this forum? Do you maybe know his username? Did (s)he participate in topics about weird backup obfuscation?
I'm out of question marks, need to resupply...