You must have had some money in the bank at the start of your PTO's year, even though your treasurer was slow to make deposits. Otherwise, you would've noticed when you couldn't pay for things your PTO was doing. That assumption leads me to lean toward to reporting only the money that was actually in your bank account during the fiscal year. The money that was delayed into the next fiscal year would be reported in the next fiscal year's 990. Are you talking about a huge proportion of your income? Probably not, again, since you didn't "miss" the money until you did your informal audit. But if I were in your situation, I would call the IRS's non-profit help line (1-877-829-5500) and discuss the situation with the rep. Then I'd call back and discuss it with another rep to see if you get the same advice (you don't always, because there are different ways to interpret and solve problems). You can have the discussion without revealing your PTO's name, so you don't have to be nervous that calling the IRS will put your PTO on some hot list. You might also want to discuss this with a certified public accountant, of which I am not.
Regarding expenses, just be consistent. It's always been my practice to recognize expenses when we write the check, regardless of when the check actually clears. That hasn't been a big disconnect for us since most of our activity ends in June, giving checks time to clear before our fiscal year ends July 31. As treasurer, I need to be able to provide information to support decision-making. If I waited to post expense transactions to our Treasurer's Report until the check cleared, I would always lag in our "actual to date" view. That could lead us to believe we had more money on hand than we really did. Again, I am not an accountant, and my advice is based strictly on common sense, not GAAP.
We had a treasurer who was doing a great job, then last spring, things started to slow down - by August, it looked like deposits just weren't being made, September reflected that when they were made, they were MONTHS behind. Now, she's stepped down, and looking at the records, we have payments that were made to us last fiscal year, that weren't deposited until this fiscal year.
Last year is our first year as a 501 3c. We marked cash rather than accrual in our 1023.
The big question - do we report the money received under the previous fiscal year, or under this year when it was deposited?
The same question for expenses - do you record the expenses based on the date the check is written, or the date the check is cleared?
Thank you, I'm sure there are more questions to come!