First of all, this is a wonderful series. BUT, I preordered this in March, 2010, as a 4-disc, Series 3 AND 4 set. Yet, what has arrived is Series 3 only. My invoice states it is a 4pc DVD , Series 3 & 4. A search of the data base shows only Series 3. What happened to Series 4? I am a big Pie in the Sky fan and this is a major disappointment