What is the meaning of “Kosher LePesach Erev Pesach” that is written on many dairy products?
Certain Hashgacha companies choose to write on their dairy products “Kosher LePesach Erev Pesach” instead of simply writing Kosher for Pesach. This does not mean that the product is only Kosher for Erev Pesach and is not Kosher for Pesach itself. Rather, this is mentioned as a stringency and expresses that the dairy product was produced prior to Pesach and is thus free of any issue of the cow being fed Chametz when it was milked, as this issue only applies on Pesach itself as explained above. The Hashgacha organization “Eida Hachareidis” as a policy does not supervise milk products during Chol Hamoed Pesach and hence all their milk products have written on them “Erev Pesach”, as they are all produced before Pesach for the sake of consumption on Pesach.
 See Madrich Eida Hachariedis for Pesach and all year under “Tenuva”