batch file with sed - escape character, trailing newlines

I'm using ssed (super-sed) version 3.59, based on GNU sed version 3.02.80. sed newbie here, so be prepared for horrors below.

I need to create a batch file to run under Windows XP which will repair broken lines in a text data file. Valid lines in the data file end in one of these three strings:
""" (three double quotes)
TEMPORARY.ID"
NEXT***"
... so I need a ssed command which will find any newline NOT preceded by one of the above strings, and remove the newline.

The naive best I've been able to do so far is:
ssed -R "(?<!\"\"\"/TEMPORARY.ID\"/NEXT\*\*\*\"\n/d" oldfile > newfile

Apart from the fact that there's got to be a way of escaping all characters in a group, there seem to be two problems here.
(1) The escape character isn't working ahead of " (it works ahead of *). The command seems to be being interpreted as finishing at the first ".
(2) It doesn't find the newline character. I found a reference to sed removing trailing newlines before doing pattern matching, but I can make no sense of the example given to demonstrate how one line should be joined to the next.

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