I think the issue, just to reiterate, is that it has been shown in research work around the world, across this country, and by very many statisticians that it is in fact the groups you have highlighted who will be less likely to participate in the voluntary surveys, and who therefore will be missed. That is not measurable, so it can fluctuate, and therefore comparisons over time will no longer be relevant. They're not accurate.
I think the statement that if you can't measure it you can't manage it is a very succinct way of summarizing the issue.