Your entries to start this year should have included all balances on all COA and Balance Sheet accounts from your previous accounting program....that being said my hunch is you have in the past been using excel at best and back of napkins in a shoe box at worst.

The income received this year has to be offset by your project costs (which were not deductible expenses in the years incurred for flips but only when property is sold or placed into rental service). Sales price less WIP (Works in Progress) costs equals your taxable gain.

In your example you will receive a 1099 for $180,000 and will need that recorded as income. To avoid paying taxes on all $180k you NOW get to deduct all the expenses of the rehab.  If you deducted those erroneously in the prior year tax return I suggest first you seek advice from your tax advisor. I cannot give tax advice but if these dollars were expensed previously then all $180,000 mightg be currently taxable in full.