Well you must know the restrictions exist so I don't think being in deliberate contravention will help. There is no requirement for the PCN to give an exact location, but if the location is wrong then you can argue the contravention alleged did not occur.
Here's a draft you can send:
Dear London Borough of Harrow,
The alleged contravention did not occur. It is alleged on the PCN that a contravention took place while my car was parked on Cannon Lane opposite lamppost 4, but my car was not at that location. Lamppost 4 is situated opposite number 9 Cannon Lane, but my car was opposite number 16 Cannon Lane. If the contravention alleged on the PCN did not occur (which it did not), it is then irrelevant whether a contravention did or didn't occur at some other point along Cannon Lane, as it is only the matter alleged on the PCN that counts.
It follows that the PCN must be cancelled.
Yours faithfully,
Send this online and keep a screenshot of the confirmation page.
In the meantime I have found the traffic order for this location, it's
The Harrow (Parking Places) Traffic Order 2020 and Cannon Lane is in
Schedule 1 on page six. The interesting thing is the order and the road markings don't match up to each other at all. I'm going to make some enquiries with the council about this, if they have simply messed up the order then we can use this argument at the notice to owner stage, or possibly at the tribunal.