How do I keep a placeholder date row sorted on the top of a sheet sorted by descending date?

First off, apologies for the poor description in the title. I inherited a lead tracking spreadsheet from someone who was (relative to me) very experienced with Excel. Essentially we have a sheet that sorts by descending dates, so the most recent entry is at the top of the sheet. The way the sheet is configured is that a bunch of cells in the Date Entered column has a placeholder date of 1/1/1900. Nearly all of these sort to the bottom of the sheet, but there was always one of those rows that we had in the top spot to fill out. Once the true date is entered and the sorting is updated that row will go to the correct spot in the list and a new placeholder row with the 1/1/1900 date appears at the top. At some point one of my co-workers did something to the sheet that stopped this from happening, and I do not know what my previous co-worker did to get that function to work because I cannot find anything in the column sort options. Thanks for the help!