Investors & landlords

Are you saying that you never had anyone look at your past K-1s to calculate what had to be reported (e.g., positive numbers in boxes 2,3,5, or 6), or should be deducted (e.g., charitable contributions) and to also calculate the suspended losses?

If the answer is no -- that you have to rebuild all your past K-1s (and I'm assuming amend prior year returns for income missed), my suggestion is to either consult a Tax Preparer or to buy past year's of TT to see how the program handles it.  And I'm really not saying that to duck the question.  Its just that codes change from year to year (e.g., Foreign Taxes paid or accrued are different this year vs last).  New reporting shows up (e.g., this year brought QBI deductions and Excess Interest reporting).  There are Sec 751 and 754 statements to file.  If you have foreign taxes, they are eligible for the foreign tax credit but that has to go through Form 1116 and a completely separate set of calculations.  And is you've already figured out, some items get suspended while others are immediately reported and dealt with.  I simply wouldn't attempt it by hand....

The only other guidance that I can offer is that, in any given year, you should be able to make your spreadsheet reconcile what the K-1, Section L shows as "Current Yr Increase (Decrease)" -- the 4th line of that section -- with all the numbers on the K-1.  Items in boxes 1-10 tend to add together, and then items in boxes 13, 18, 20T(depletion), 16 (only the taxes paid or accrued) get subtracted from that.  Its a bit of a game, figuring out which codes can be ignored vs which ones figure in.  And it doesn't tell you what's suspended vs recognized.  But it at least shows you every number that "counts" -- that need to be figured into your taxes one way or the other.

EDITED TO ADD:  Here's one other random thought that may get you 90% of the way there, and save the expense of the prepare/past years TT purchase.  Created a dummy return in this year's TT.  Enter the first year's K-1, and see what it does to your taxes (items transferred to the return vs suspended).  You may have to play with some of the codes to get them to match up if they were different in prior years, and definitely ignore anything with QBI, but you'd at least be able to see (looking at the K-1 worksheet in Forms mode) how the suspended losses work.  Then repeat for the second year, etc.

That won't solve the issue of amending (if required), and it will probably allow you to calculate your suspended losses to a pretty good accuracy.