Got it. Yes, Greg even calls it "a place-holder". You should email him your question. I'm a non-tech pleb and he has answered my questions in the past.
I read the blog post you linked, but I still don't understand. In the attached screenshot, the blog states that the reason for putting the previous locking script in the empty signature space is to indicate that we recognize the original locking script. Does that make sense? It's not hidden information; anyone can find it since the txid and vout are specified.
https://cdn.nostrcheck.me/ebc5fb4ccd63e238945f8877738de1f0f16959017feea3dc7c62c2569bb64596.webp
https://cdn.nostrcheck.me/cb5a012f01d420be5284a75ee2ff66c310b26abe4028ce7ce50ce3d7b080f0af.webp
Discussion
Right, I’ll follow your suggestion and ask by email. The blog looks very professional, and I think he’ll be able to answer my question well. Thanks for recommending
post the answer
Don’t rush. I still haven’t gotten an answer, lol.
I asked that person about the question, and he also didn't think there was any particular reason it had to be that way. It seems likely to be one of those things in Bitcoin’s history that weren't technically necessary, but were simply implemented by Satoshi that way—and now it can't really be changed, so it's just left as-is. Looks like my guess was right.