The most important things are that you filed and extension and won't owe any taxes when the k-1 is finalized.
Is there any official guidance from the IRS or any relevant tax authorities on handling situations like this? There is none. This is a common occurrence with some investments where due to the complexities of gathering all relevant tax data it's not possible for them to file any earlier
My CPA advises waiting to file my tax return until I receive the K-1. On the other hand, I've seen discussions on online forums suggesting it's acceptable to file my return now and then submit an amendment later, once I have the K-1.
I agree with your CPA it's kind of silly to file an estimated return and then file an amended return. If you are using a pro to do your return, then you would have to pay to prepare the estimated return and then pay for the additional time it takes them to prepare an amended return. It you file an estimated return and get a refund and the final k-1 now results in you owing there will be penalties for late payment. 100% of your actual tax liability was due 4/15/2024.
the only reason I could see filing an estimated return is if you didn't pay in on 4/15 the taxes that would result from including the results of the k-1.
if you file now and amend in September and are due a refund, you would likely not receive it for at least 3 months probably longer.
