Link Lab
Every link below goes to the same place carrying the same short code — k4p2m9 — the one thing that says this click came from here. Only two things change: where the code sits, and who writes it down.
Pretend this visitor has
With nothing in the way, all four work. Turn something on.
site.com/page?id=k4p2m9
a script on the page writes it down
site.com/page?id=k4p2m9
the server writes it down on the way
site.com/k4p2m9
a script on the page writes it down
site.com/k4p2m9
the server writes it down on the way
Only one design survives both: the code in the path, written down by the server on the way through — variant D. Everything else depends on a script that can be blocked, or a parameter that can be stripped, before anything is recorded.
That is the gap between what your ad platform reports and what actually happened. It is not a rounding error, and no amount of dashboard tuning recovers a click that was never written down.
This is a model of the two failure modes, not a live network test — it runs entirely in your browser and sends nothing anywhere.