Bruce,
I believe your missing days are due to the 48 years at only 365 days a piece.  The length of a solar year (tropical) is 365.24218.  If you multiply the 48 years times the .24218 it totals 11.624 days.  Add the 11.624 days to your count of 17,629 and you come to the 17,640th day.  Another way to look at it is you missed twelve leap days (February 29) between 1967 and 2015 in which the year length is 366 days.  Plus or minus 1 days can easily be explained by differing time zones around the world.  

YBIC,
Kevin H.