However, Hamodia is reporting this week that it is all a fake. It is practically impossible to keep this chumra as manufacturers can put whatever they want on the label and no one checks whether it is actually true.
Kashrus organizations do not see a difference between cake sold halachically to a gentile and beer ... For that reason there are no grounds for relying on the manufactures declarations.
Halachically there is no problem with eating chamtez that was sold to a gentile in accordance withthe law. ... So the kashrus organizations stance is usually to permit the manufacturers to write on the package whatever they want
In other words the Kashrus organizations like the Eidah Hacharedis, R' Landau, R' Rubin and others hold that this is a chumra with no basis and therefore have no issue with the manufacturers writing whatever they want.
In short, this is a chumra that makes people feel frum but has no basis in halacha and is in fact not really possible to keep.
Some people rely on checking product codes which tells them when the product was made. This year for example, a code higher then 9106 (9 - 2009, 106 the 106th day of the year) means it was made after Pesach. However, this is not that useful. All it says is that the product was made after Pesach. However, every Chometz product has chometz ingredients in it (at least flour which is most probably chometz because it was washed) and the consumer has no way of knowing when the chometz ingredients were made. For example even if you only buy cookies that were made after Pesach you have no idea what flour was used. It is very possible/probable that the flour used to make the cookies was chometz and was sold for Pesach.