Hi Tara,
It would be great if you can provide some examples.
ACWP usually shows incorrect values when you make a change to the rate matrix and before running the Rate Matrix extraction, Update Cost Totals or Post Timesheet is executed.
If you are looking at ACWP at a project level or task level and you find it incorrect, can you please check and make sure the As Of date (usually set at Project Properties - Schedule sub page) is not set. If you have As Of Date set, then the ACWP will be calculated until that date. If its blank then its calculated till the current date. Also check if you have actuals in the future - because ACWP for future actuals will not be calculated unless you have As of date set to future.
Thanks,
Jerin