Hi Brian
I have just opened the file in question on my Imac at home 10.6.8 running LO 4.2.4.2.
The default User interface is English USA, Local Setting is UK, and default currency is GBP, ill check the laptop & works imac tomorrow for specifics etc
The alterations i did earlier after i sent the first email are still intact 
I understand that the NNNDDD etc are not stored with in the format, but just wondered where the jewish annotations came into effect? ive never used them in the past, my laptop is setup for UK english, and it was all working fine last time i looked at that particular area? And there definatly was no jewish annotation in there?
the top reference in the list of pre-set annotations mentioned above is
[~jewish]NNNND MMMM YYYY, and in the format box it is "Friday 22 Tevet 5760" and in the preview box it is "Monday 9 Tammuz 5774", i dont even know if thats correct? or if the jewish calendar works on a different format?? If there are any jewish memebers out there reading this, let me know please 
There appears to be 10 with in the list, that appeared, and the one that i defined manually "NN D" appears after them?
ill check with my works mac in a bit, i know i opened the file there, its running ver 3, ill double check its set for UK etc, but i normally make a point of changing the locale to UK, saying that it was a long time ago Ver 3 came out, and i cant remote log in to check etc.
I do know that was not the cause of the corruption, as i emailed the file over to a collegue to review the work, and he said the formula made no sense, so i loaded it on the Ver 3 at work, and saw the corruption etc.
I have also as a test just copied the cell into a new spreadsheet, and it took over the jewish annotation?
i then created a new spreadsheet, and just entered a date, and changed its format, and there was no jewish annotation?
but ive never used any other computer apart from the laptop to open the file, ive copied/emailed to others or opened from dropbox, but not saved it, apart from the one time mentioned above, when the corruption had already occured.
I was just looking for insights as to whether anyone else has had the problem? i just dont want to go much further, and loose the lot, thinking about it, ill see how many revisions i can go back on dropbox, and see when it happened...
Sorry guys if some doesnt make sense, my eyes are hurting, and its late, and i was a tad annoyed earlier when my boss said i want those sheets and im like ARRRRGGGHHHHHH
cheers
Phil