Who sets cjevent, and when
cjevent is added by CJ Affiliate's own redirect servers at the instant someone clicks a publisher's tracking link, not by the merchant and not by the publisher's own code. By the time the browser lands on the advertiser's site, the value already exists, generated entirely on CJ's side.
What it identifies
cjevent marks a single click, tied to that visitor's session at the moment they clicked, rather than a person or a whole campaign. It is an opaque, case-sensitive string. It survives a normal redirect chain intact.
Why an old link can still look valid and no longer count
cjevent itself carries no expiry stamp. It is a static token, minted once at the click, and it will sit in a bookmark or a forwarded email looking just as valid a month later as it did on day one.
What actually has a shelf life is the advertiser's cookie window, a setting each merchant configures separately inside their own CJ program. On a first visit, the merchant's site is expected to read cjevent from the URL and store a reference to it in a first-party cookie. At purchase, CJ's tag reads that cookie and reports the sale back for commission. If the original click happened outside whatever cookie duration that particular advertiser set, the commission does not get credited, even though the cjevent string in the old link still reads as a perfectly normal token.
So the link itself is not expired in any way you can see. Whether it still pays the original publisher depends on a setting you cannot read from the URL at all.
What a stripped link costs
A visitor sees no difference. The page behaves the same whether cjevent is there or not. The cost lands on the publisher: without cjevent, the advertiser's site never sets that first-party cookie for the visit, so even a same-day purchase cannot be traced back to the click, and the commission is lost outright rather than just misreported.
irclickid and awc are the other two affiliate click IDs built the same way. See irclickid and awc, or start from the link decoder to pull cjevent out of a real URL.