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@JB4797 Yes on 1 and 2

Technically, your basis in the partnership is "unified" -- each sale is pulling from every lot you bought, for a combination of short and long term.  So even though your broker will allow you to do FIFO, it doesn't meet the letter of the IRS requirements.  To illustrate, suppose you bought 1000 shares 10 years ago, and 100 shares yesterday.  If you sell 110 shares tomorrow, it would have to be treated as 100 from the old lot, and 10 from the new lot.  The sales schedule would show this as a 90%, 10% split on the basis.  And your broker would report it as both LT and ST. 

So with that said, you have a couple options.

1) If you contact the K-1 preparer (contact info should be in the K-1), I believe they'll reissue the Sales Schedule using a FIFO calculation.  This won't meet the letter of the IRS reg (which the K-1 discusses somewhere in their fine print), but that's something a tax expert could advise on.

2) If you contact your broker, they may reissue the 1099-B to reflect average cost (giving you some short term transactions instead of everything being long term).  I suspect they won't though, since too much time has passed

3) Depending on the dollars involved, the 5% that should be short term may be inconsequential.  In that case, you could decide to simply not bother adjusting.  This is NOT tax or legal advice -- just an observation.

4) You can do your own calculations of what the 1099-B should have reported (assuming you made every sale pulling proportionally from each lot), and then use the 1099-B interview to adjust what the broker sent you.  You'd probably want to include a statement explaining your adjustments.  I haven't done this myself, so if you go this route I'd suggest posting it as a separate question on the forum to get some better advice on how to handle it.