sed or awk or perl + remove all not uniq lines except the first line (FILE NAME) + shell script

I have the following file How to remove by sed all FILE NAME lines except the first uniq FILE NAME For example need to remove all FILE NAME lines from the file except the first:

FILE NAME: /dir1/dir2/dir3/dir4/dir5/file

FILE NAME: /dirA/dirB/dirC/dirD/dirE/file

the file:

FILE NAME: /dir1/dir2/dir3/dir4/dir5/file

PARAMETER NAME: blablabla

TARGET FILE: 12

SOURCE FILE: 565

FILE NAME: /dir1/dir2/dir3/dir4/dir5/file

PARAMETER NAME: blablabla

TARGET FILE: 18

SOURCE FILE: 552

FILE NAME: /dir1/dir2/dir3/dir4/dir5/file

PARAMETER NAME: blablabla

TARGET FILE: 14

SOURCE FILE: 559

FILE NAME: /dirA/dirB/dirC/dirD/dirE/file

PARAMETER NAME: blablabla

TARGET FILE: 134

SOURCE FILE: 344

FILE NAME: /dirA/dirB/dirC/dirD/dirE/file

PARAMETER NAME: blablabla

TARGET FILE: 13

SOURCE FILE: 445

FILE NAME: /dirA/dirB/dirC/dirD/dirE/file

PARAMETER NAME: blablabla

TARGET FILE: 13

SOURCE FILE: 434

awk '!(/^FILE NAME:/ && seen[$NF]++)' infile

In python:

import sys
seen = set()
for line in sys.stdin:
  if (line.startswith('FILE NAME: ')):
    if (line in seen):
      continue
    else:
      seen.add(line)
  sys.stdout.write(line)
sys.flush()

I'll have a think about sed and get back to you in a few hours, hopefully.

To be honest, though, this is not a very seddish task - sed likes tasks where you can process each line based only on the contents of that line (and perhaps one thing you've seen before and put in the hold buffer). This job fundamentally involves a more complex body of knowledge that needs to be carried through the file.