There are corrections and movements to old cases every day, tests removed, tests added, I suspect some of it may even be fluctuations that happen every day. Most times this has little impact on the headline figures as it's added one day removed another.
In recent days there has been a lot of fluctuation on the unconfirmed LFD's, almost certainly due to the realisation that they need to remove false positives to be at all fair with the figures, and the adjustments here are considerably more significant.
Dashboards are never accurate, they can often be deliberately misleading, in general I think dashboards are overall harmful, because too many people use them superficially. However here data is generally pretty good, look at cases and deaths by specimen date though, that's the important thing, not the announced date.