How come DD didn't know about Snapes patronus?

[pforparvati]

No: HPFGUIDX 172620

Hello all....

          I was surprised to find that DD didn't know about Snape's
patronus until Snape himself showed him. After all the years working
for order,especially after GoF when Order was recalled and started
working, how it was possible that DD never got a message in the form of
Snape's patronus until HBP. I assume that memories Harry saw in the
pensieve[DH] were in sequence. Since this memory was after the memory
of Snape arguing with headmaster in the forest[HBP] in which DD asked
Snape to come his office so that he can show how much he trust Snape.
In that night meeting, Snape showed Dumbledore his patronus...Isn't it
strange that this happened in HBP...


profParvati,
feeling more disappointed to find the way Snape's Death
occured...certainly one of the best DADA teacher like Snape deserved
more fight than this...