If the actual input to a transaction (in Monero terminology this is the output of the prior transaction) is not also an input to another transaction's ring signature (and when all the other inputs to the ring are spent) or if it is also the input to a subsequent ring in which all the other inputs were outputs created after the said transaction was created, then the anonymity of the said transaction is entirely unmasked.
This is really
what MRL-0004 deals with (the section on Temporal Association attacks).
A lot of this changes with the recommendations MRL4 made, which will come in a hard fork later this year (once we've established a forking strategy, per
this forum post).
I don't check this thread, so if you reply and don't hear back from me in a couple of days just send me a PM nudging me:)