I'm not sure. Are there even any quotes out there about "the shelf" from GAs? This might just be something that has spread among the membership trying to cope (or NOT cope) with the widespread availability of absolute proof that their church is false.
Anyone with any curiosity and access to the internet can find solid evidence that Mormonism is not true within 10 minutes. "The shelf" might just be a natural reaction to this proof. The human mind cannot accept two contradicting facts at the same time, so one or the other has to go. But you can't just forget that you ever learned a fact, and you cannot disprove the truth. If it can't be destroyed and they will not confront it, then it must be ignored. What else can they do with it?