Updating our memory requires its original context.

Here is some fascinating work by Hupbach et. al. A clip from a Science Magazine summary:

Recent research has shown that reactivating apparently stable memories can render them fragile and open to modification and to another round of stabilization in a process called reconsolidation. Hupbach et al. explored the conditions leading to the updating of episodic memory. They found that memory plasticity at reactivation provides a mechanism for updating memories, and that the latter are determined by the spatial context; that is, the "where" of episodic memory. Only when the memory was reactivated in the same context as when it was learned could new learning be incorporated into the existing store of knowledge; if reactivated in a new context, no updating occurred.

The abstract of the work:

Understanding the dynamics of memory change is one of the current challenges facing cognitive neuroscience. Recent animal work on memory reconsolidation shows that memories can be altered long after acquisition. When reactivated, memories can be modified and require a restabilization (reconsolidation) process. We recently extended this finding to human episodic memory by showing that memory reactivation mediates the incorporation of new information into existing memory. Here we show that the spatial context plays a unique role for this type of memory updating: Being in the same spatial context during original and new learning is both necessary and sufficient for the incorporation of new information into existing episodic memories. Memories are automatically reactivated when subjects return to an original learning context, where updating by incorporating new contents can occur. However, when in a novel context, updating of existing memories does not occur, and a new episodic memory is created instead.