Complex sentence: Beichuan Middle School and Yingxiu Primary School could have passed with fortification intensity of VII liedu had they been built after 2004; but because they were built before the publication of even GB 500011-2001, they could be using older standards or none at all.
Split into simpler sentences: Beichuan Middle School and Yingxiu Primary School could have passed with fortification intensity of VII liedu had they been built after 2004. Because the latter were built before the publication of even GB 500011-2001, it was using an even older standard, or none at all.