Actually, the SSPXers (with apologies to St. Pius) who attend the local chapel, Our Lady of Fatima, insist that the Church teaches heresies. As do my family members in St. Mary Kansas and Post Falls, Idaho. They insist that the Catechism is filled with heresies as well as the GIRM, for starters. I have no idea how this reconciles with Christ's promise that the gates of Hell will not prevail against the Church. But they say it, over and over and over again.
"Really by whom?"
His name is Daivd....
The CCC is not the Church. The GIRM is not the Church. Neither have any promises of being infallible. Both can be riddled with error and it would not mean that "the gates of hell have prevailed."