Problems in MS Word formatting bibliograph for bibtex export

All my references have valid label fields which appear in endnote and in word field codes and can be generated in the bibtex references from endnote successfully and can be read by a bibtex compiler (ie no commas spaces etc), but when I format the bibliography for bibtex export in MS Word some references it adopts the label and others it ignors it and so far I can see no pattern to identify the bug or my misuse of the software.

So, as a result of the format processing, in most places I see in the text in MS Word I see \cite{xxx_xxx_xxx} and in the bibliography at the bottom of the word document I see a series of bibtex references each with a label.  However for a few of these references the label is missing and in the text there is no ref just a blank!  I cannot see what is different about these labels, they are in endnote and appear to be fine.  If I add them into the relevant bibtex ref and add the \cite ref to the text and then use this text and this bibliography in latex, the code is successfully compiled by a bibtex and latex compiler.

Therefore I cannot see why a few of these refs do not format to bibtex in word.  It is very frustrating since I get no warnings after the format and so I have to check the document meticulously manually to find out which refs have been missed.

I freely admit I have never used bibtex compiler or latex, but aAre you unlinking the fields and making a copy, prior to performing these tasks?