It's one thing if it were typed in, but this is not typically from typing, it's from opening a CSV file that has a field that's OCT4. (And honestly, if I want a date, I'll hit the date formatting button, Excel.)
It is super hard to figure out a way to import data into excel without triggering auto-conversions. I knew a way a few years ago when I was dealing with lots more biologists, but I have forgotten now. If I had to do it now, I would write XLSX directly then manually check the file in Excel, because Excel is fundamentally untrustworthy.