Don't assume anything from the data sheet of a sigma delta ADC. There used to be many that looked OK at first sight, but had a variety of quirks when you got into the details. In weigh scales you need a lot of resolution, so these quirks can be really important. Performance drifting over time affected quite a few, especially some of the early Chinese ones. A DC offset that drifted a lot, or moved in fairly sharp steps for no obvious reason, was common. Over time things have improved a lot, but when you have one of these problems it can take ages to properly diagnose. I'd try to find what everyone else is using successfully in your application, and look carefully at that part. If its a part that has been through a number of revisions you may find early ones were quirky, and newly produced parts are great. It can be a minefield.