If every occurrence of the string " End" reliably marks the end of a record (that is, if no record ever includes " End" as part of the internal data), you could just set $/ to this string, and read just one complete "record" at a time:

{
   local $/ = " End";
   while (<>) {
      s/.* Start//;
      chomp;  # removes $/ (" End") from end of string
      print;
   }
}
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