How to extract characters from a cell in Excel?

kind regards

I am working on some data and I need to extract from column A:A exactly only the dates that start in 2017 and end in number, that is to say with a length of 8 characters [20171015], the problem is that I am performing this operation in column C:C but due to the extension of some characters in some rows it does not bring me the totality of numbers that I am requesting. Is there an additional method to make this possible or can I fix the formula that I am using in a wrong way?

I appreciate your collaboration.

PS: the formula I am using is =MID(A9,FIND(" ",A9,B9+1),9)

worksheet

In B2, formula copied down :

=-LOOKUP(1,-MID(A2,FIND(2,A2),{7;8}))