I don't know why suncream manufacturers do not put a sealed lid on the bottles as its usually 12mths from when first opened. Also they should put a date of manufacture or expiry instead of codes, every year I end up ringing the companies when checking out the unopened ones that I would have left over from the year before.
I always go to the back of the shelf when buying suncreams and then I seal the lid with selotape when I buy them so that I know that they have not been opened (hopefully no one opened them in the shop for a smell!). I usually seal all bottle tops for packing anyway in the hope that if they get squashed they won't open.