Items listed on your Chronicle sheet are considered "always available". In other words, they join low-level potions, scrolls, weapons and armor as things your character can buy at any time.
From the Guide to PFS Organized Play (p. 18):
Every item listed on your Chronicle
sheets is considered always available for purchase for you,
regardless of whether it’s on your first Chronicle sheet or
your 21st Chronicle sheet. The only exceptions are items
that have a purchase limit. You may never purchase more
of that item throughout the life of your character than
the number amount listed as the purchase limit.
As it says, exceptions to the "always available" default will be noted explicitly, either as a "purchase limit" or with a note like, "cross this item off of your Chronicle sheet after it has been used."