The indicative *can’t* be right unless you’ve never withdrawn/BILed/otherwise changed a learner.
Almost by definition, withdrawals are reported at least a calendar month after they happen, so some money for that learner will be clawed back. The indicative report isn’t clever enough to know what has happened previously, only what happening in the current file, so it doesn’t know where you’ve been overpaid.
…and that’s before we get to levy employers who have run out of levy and so switch to 95/5 which, again, the indicative report can’t know about.
The least worst way of doing it is keeping a running total of what you’ve been actually paid and take that amount from the total the indicative report is telling you to get a better idea of what should be coming your way (still not going to cope with the exhausted levy issue, but should be closer).