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As a lawyer, I would counsel a food manufacturer client (if I had one)
that unless it can be absolutely, dead certain that its product did not
contain gluten in any amount, it should decline to tell anyone whether or
not its product is gluten free, because of the product liability potential.
I suspect that the larger the company, and the bigger its product line,
the more difficult it becomes for that company to be absolutely, dead
certain.  I suspect that the larger companies use many different sources
for ingrediants, and will order from one or the other depending upon
supply and price.  They undoubtedly have specifications for those
suppliers, but I doubt that "gluten free" is one of them (except for those
few who cater to the celiac market)!  I am sure that the cost of tracking
GF status of all these ingrediants, and changing labels to fit the source
of one or more ingrediants, is a cost that most manufacturers will find
difficult to justify, based on the number of people they perceive to be
affected.  Those who pursue labelling laws will have to be careful,
because I would expect manufacturers to respond that they should be able
to say "GF" or "not GF" on their labels, and that they wouldl push to have
the right to say "not guaranteed GF" if that can't, or don't want to,
certify GF or non-GF status.  Because we are able to protect ourselves by
not eating food when we don't know for sure whether it is GF, it may be
very difficult to persuade the industry and the government that
manufacturers should have to bear the cost of determining and disclosing
whether their products contain gluten.  Although it is not satisfactory to us,
under a strict cost/benefit analysis, an industry response of "don't buy
it if you don't want to" may be deemed to be entirely reasonable.