I think i know what you mean, I had a problem where i separated each user with the date in numbers followed by "." and a random number.
everytime i exported it into a spreadsheet the numbers were formatted by excel kept round up the numbers and shortening my uniqueid, this was extremely frustrating.
the only thing i could do was open spreadsheet and import via database, but i selected the column which was for uniqueid to text formatted.
Have tried placing this single quote before the numbers ( ' ) see if that works? trick the worksheet into thinking it is text?