How do I read the WIP schedule?
Each job at a month end: how far along it is, what that has earned, what you billed, and whether you're ahead or behind.
The WIP schedule works out each job's percent complete from cost: what you have spent so far against what you expect the job to cost in all — your own estimate if you set one, or cost so far plus the job's forecast remaining. That share of the contract (with every approved change) is what the job has earned.
Cost so far is the approved weeks' hours at each person's cost rate, cut at the month end by the days actually worked, plus approved expenses. When a contractor's week has been paid, what you paid counts instead of the estimate, never on top of it.
Billed counts every invoice dated by the month end, before retainage. Billed ahead of the work means you have collected ahead of what you have earned; billed behind means you have earned more than you have billed. A job whose expected cost is above its contract carries the rest of that loss now.
Switch the view to work the records prove to compare billing against the hours, inspections and per diem days on record instead of cost.
Lock a month once it has ended and it is kept exactly as it stood, even as late time or invoices land. A correction is a new revision; the earlier one stays. Only your admin sees this schedule.