Four certificates expired on me because I never diaried the deadline to start foreclosure
Small portfolio, 46 certificates across three counties at the peak, and I found the ceiling in the least interesting way possible.
In my state a tax certificate has a life. If the holder doesn't begin the foreclosure or deed application process within a fixed number of years from the certificate date, the certificate expires and the county keeps the money. The exact period and the exact triggering act vary by state and sometimes by the type of sale, and I'd read that sentence in a book two years earlier and treated it as trivia because everything redeems anyway.
Forty-two of my 46 redeemed. That's the part that killed me. Every quarter the redemptions came in, I updated the spreadsheet, and the four that never paid slid down the sheet below the row where I stopped scrolling. No system, just habit and attention, and my attention was on the ones that were paying.
What expired: four certificates, $7,940 of face, plus subsequent taxes I'd advanced on two of them, another $2,610. So $10,550 gone with no recovery and no property. Two of those parcels were vacant land I'd have been happy to own at that basis. One was a small house that a title search would probably have shown as a mess. I'll never know now.
The cause I'd name is that I never separated the two businesses I was running. The redemption business needs a spreadsheet you look at when checks arrive. The foreclosure business needs a calendar that fires whether or not you're paying attention, per certificate, at a date computed from the certificate date and not from anything I do. I ran one business and pretended it covered both.
What I'd do differently. On the day a certificate issues, I'd enter two dates in a calendar with alerts: the date I start the deed or foreclosure process, and a date six months before that where I decide whether the parcel is worth the legal cost. I'd also stop advancing subsequent taxes on any certificate I hadn't already decided I'd foreclose on, because advancing money into a certificate I had no intention of enforcing was throwing good money at a position I'd already abandoned without admitting it.
And I'd confirm the expiration rule for each county in writing at the start, because two of my three counties describe the triggering act differently on their own websites.