Extrapolation

Hi,

I have a question regarding extrapolation.
Its hard to formulate the question, so I asked a couple...

I know what extrapolation means, but I have the below scenario which I need some clarity on:

We have to do 6000 surveys in a month.
I only manage to do 5000.
Based on the 5000, do we extrapolate the data to "look" like 6000?
In other words the 5000 in fat becomes 6000?
OR
Based on the 5000, we extrapolate the data to make future decisions (trends) based on the data. Almost linear...something going forward.

So does extrapolation of the 5000 means it makes it 6000 or can we only predict future trends based on the 5000.

If we can use the 5000 to make it look like 6000....then surely you can use 1000 instead of 5000.
What is the statistical minimum of the sample based on the size of the universe? (Ratio)

Thanks!!
John