Renumber rows with the inclusion of blank

You are asking for Excel to create the 'missing' position values and then put a 0 in the column next to it. An automated way would require VBA, since Excel will not create data for you. The 'easier' way is for you to create the list of integers 1 to 18 (or whatever your max Position value is) in column C. Then in D1 use:
=IFERROR(INDEX($B$1:$B$18,MATCH(C1,$A$1:$A$18,0)),0)
and drag down the column

Based on your last post in this thread, its apparent that you are satisfied with the solution(s) you've received and have solved your question, but you haven't marked your thread as "SOLVED". I will do it for you this time.

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I hope this isn't against the rules (posting on a solved thread), I was following this post and after reading Pauley's solution, I wondered if you already created the list as you note

create the list of integers 1 to 18 (or whatever your max Position value is) in column C

wouldn't a find and replace work as well and maybe a little more quickly? I tried it using find (left blank) and replace 0 and it worked for me and was pretty easy and quick.

would think it would work for a long list too but don't want to try it to see.
Cool.