Counted my 180 days from the wrong date, so the deferral evaporated

This is the failure mode I see most in the docs. Subscription agreements almost always make the investor represent that the investment is being made within the applicable period, and then disclaim any responsibility for determining what that period is. So the fund has no reason to catch your error and every reason not to. The rep is yours.

If you're ever in the pass-through situation again, ask the partnership in writing whether it intends to make the deferral election at the entity level, because that decision changes the analysis for every partner underneath. I've seen a GP make that call in February and inform partners in April.

The mechanism is worth stating cleanly, because rigging's situation is common and the timing rules for pass-through gains are genuinely different from a direct sale.

When you sell an asset yourself, the reinvestment period generally runs from the date of the sale. When the gain comes to you on a K-1 from a partnership or S corporation, the entity itself may be able to make the deferral election, and if it doesn't, the partner's window can start from a different date tied to the entity's tax year rather than the transaction date. Which date governs depends on who elects and on the entity's year end, and that determination is a tax question for a licensed preparer, not something to settle from a forum post or a fund's marketing material.

The practical consequence for a capital allocator is sequencing. The eligible start date is an input to fund selection, not an output of it. If your gains routinely arrive through entities you don't control, the operational work is establishing, in writing and before the year closes, who is making the election and what date the clock runs from. Building that into your annual process matters more now than it did a few years ago, because the One Big Beautiful Bill Act made the incentive permanent and replaced the fixed deferral deadline with a rolling five year deferral for post-2026 investments, so this becomes a recurring cycle rather than a one-time decision.

One more thing rigging got right by accident: the fund released him without penalty. Not all subscription documents work that way. Check whether yours has a break fee or an obligation that survives a failed election, and confirm the current rules with your tax professional in writing.

The part that would've got me is assuming December. I'd have done exactly the same arithmetic on the back of an envelope and never questioned it, because the sale date is the obvious date. How much notice did the partnership actually give you that the sale was happening at all?

rigging, you said the fund released you with no penalty. Was that in the document or was that goodwill? I've read subscription agreements where a failed close inside the offering period still owes an administrative fee, and one where the investor's rep about the reinvestment period survived termination, which means the fund can point at you later if the IRS ever asks the fund questions about its investor base. The new QOF reporting requirements make that less theoretical than it used to be, since the fund has to report more about who's in it.

Worth pulling your copy and reading the termination clause even now.

I've got no experience with any of this, and this thread just taught me that the gain having a start date is itself a thing you have to establish. I'd have assumed it was printed on something.