Changing as she goes along.

[Scott]

No: HPFGUIDX 12482

Just how much does JKR change/add things as she's writing. Also how 
much is planned ahead. The case in point which seems to have been 
discussed lately was why Filch is at Hogwarts if there are so many 
House Elves.

Wasn't it stated that SPEW was NOT originally planned but that Jo 
added it in whilst writing GoF? 

It seems pretty obvious that Dobby is a part of the overall plot, and 
Winky also seems to be. What about the other house elves. When Jo 
created Dobby did she think about HE's being at Hogwarts. 

How much did she plan? I think that, whilst she always knew there 
were HE's in the wizarding world she had never considered that there 
were any at Hogwarts. If she had then Filch would most likely have a 
very different role or not be in the books at all. He's not very 
central to the plot besides being a great comic relief character...

Question: Is Filch an "overseer" of the House Elves?