Two different things happen to a slate once it's over, and it's worth knowing which is which.
Your results are permanent
Every entry you've recorded a result for — stake, rank, winnings — is kept for as long as your account is. That's what feeds your net, ROI and cash rate on the Bankroll page, and it is never removed on a timer.
So the numbers you actually care about — how you're doing over a season, whether that new stack approach is working — don't expire.
The live board is kept for 30 days
The full replay of a slate is a much bigger object: every player, every score change, the trajectory chart, the whole event feed. We keep that for 30 days after the slate is played, then remove it.
After that the slate stops opening as a live board, but the entry stays in your bankroll history with its result intact.
The one case where something is lost
An entry you never recorded a result for goes when the slate does. There's nothing to keep — no stake, no finish, no winnings — so there's nothing to add to your history.
If you play a slate and don't get round to entering the result, do it within the month. The Bankroll page shows a running count of entries still waiting on you.
Why not keep everything
Honestly, storage isn't the reason — 30 days of slate data is a rounding error on our bill. It's that a board six months old is a snapshot of a night that's over, and almost nobody opens one. Your results are the part with a long life, so that's the part we treat as permanent.
If you want a slate kept beyond the window, screenshot it or export your lineups — and tell us, because if people actually want it we'd rather know.