American Express website CVS download Tiller Download

I am working on backfilling data from my american express cards and I’m noticing that Tiller is using different transaction dates than American express. It could be post date vs transaction date. It looks like the transactions are recorded as a few days after the American Express CSV download. This doesn’t apply uniformly however. Some are the same and some are a few days after. Perhaps its the credit card processor but even Amazon is all over the place.