I have been able to reverse crediting errors made by several different airlines over the years (e.g. SQ website is notorious for overriding your selected FFP with your Krisflyer account if you were logged in).

Sometimes it can be quite painful (and does not always work) and take a long time to be fixed, but I'd say most of the time I have been able to correct the mis-crediting. I don't bother if the miles aren't much because of the hassle factor.