47 days between when my management software records a vacancy and when the actual notice to vacate was filed, and I cannot find that gap anywhere in the books

There is no universal standard here, and that is a real problem for anyone trying to produce comparable numbers across a portfolio.

The three dates you are describing each measure something different, and the choice of which one anchors the books changes the vacancy cost figure materially.

Notice date (when the tenant files the legal notice to vacate) captures the moment the operator first knew the unit would turn. It is the earliest signal, so it gives you the longest apparent vacancy window and the highest apparent cost.

Move-out date (when the tenant physically leaves) is when you actually lose rent. Most ledgers default to something near this, which is why your management software often trails the notice filing by weeks.

Unit available date (when the unit is rent-ready after cleaning and repairs) is what many operators actually care about for leasing performance, because it is when you could theoretically collect rent again.

Each one is defensible depending on what question you are asking. If you want to measure legal exposure or early-warning response time, notice date matters. If you want to measure rent loss, move-out date or unit available date is more defensible. If you want to measure turn efficiency, the gap between move-out and available date is the number.

The gap in your books most likely exists because your property management software is recording one of these dates and your general ledger is recording a different one, and nobody mapped them together when the systems were set up. A bookkeeper specializing in real estate would recognize this as a property-level tracking problem, and the fix is usually defining which date triggers each entry and documenting it in a written chart of accounts policy so every property uses the same convention.

For your side project, which date are you currently treating as the canonical vacancy start, and are you pulling that from the legal filing system directly?