[chrismorgan]

RFC 2616 is long obsolete; the section you cited is now https://tools.ietf.org/html/rfc7234#section-6 and is substantially reworked. The chunk you refer to has been removed, because it no longer reflected reality in any way. Even as originally specified, as a SHOULD, it wasn’t ever practical to implement completely because of memory requirements. Since 1999, a lot has changed, and the fact of the matter was that the original recommendation just didn’t make sense any more, worded as strongly as it was. So instead they’ve switched it round to essentially say that you may redisplay an earlier-retrieved representation (rather than that you SHOULD NOT do the opposite).