It's rather hard to run tests when all we have are screenshots to work from. I'm not about to transcribe those images into actual text. Care to post some actual data in text format?
In any case, I'm not entirely clear on what you're asking. In your examples all entries in c1 are the same, and I don't see any duplicate lines in the output screenshot, only duplicates inside c4. If I understand correctly though, you want to replace everything in the c4 column with sequential numbers? That should be possible with awk. Something like this, perhaps?
Code:
awk 'BEGIN{format="%s %s %s JUNC%08d %s %s %s %s %s %s %s\n"} ; { i++ ; $4=i ; printf(format , $1,$2,$3,$4,$5,$6,$7,$8,$9,$10,$11) }' merged-file
It's kind of messy though, because I assume you'd want to properly zero-pad the entries, and my knowledge of printf in awk is limited. I can't figure out how to do it without defining every field separately (if that's even possible). Perhaps someone with more experience can come along and simplify it.
BTW, it's not usually necessary to use cat and a pipe with wc (or most other cli tools for that matter). It can take a file name as an argument.