If internalism in its various guises fails to generate an adequate account of the justification of memory belief, then we should consider externalism. Since reliabilism is the most plausible and popular externalism theory, we'll do well to put our focus there.  Loosely, reliabilism claims that a belief is justified if it is the product of a reliable belief-forming process. Perhaps, then, we should say that a memory belief is justified if it is a product of a reliable memory process.  As long as we are thinking of reliability as propensity to generate truth rather than as a measure of the track-record of a process, then a process's being reliable is a synchronic property of that process.  So will the reliabilist believe that the justificatory status of a belief earlier is irrelevant to its status as a memory belief?  No, she won't.  The reliabilist will think of memory as what Alvin Goldman has called a “belief-dependent process” (Goldman 1979).  The input of the belief-dependent process is a belief.  Memory belief is (normally, at any rate) belief that has been kept in memory.  So a reliabilist will hold that a memory belief is justified only if the memorial process that maintains it is reliable and if it was justified when originally formed.  To hold otherwise would be very much out of keeping with the spirit of reliabilism. 