As a local elector it would just need an email pointing out the error.
The PC really DO need to remedy this for the sake of the AGAR and it is a really simple fix.
Conversely, unwillingness to welcome, acknowledge and act upon polite suggestions and/or observations and the accrual of a number of basic admin errors is often a combat indicator of more systemic procedural carelessness
It might not be at the very top of the priority list, but the ‘goodwill’ that could be generated by acknowledging and thanking a member of the public for their observation would be a sign of an engaged and proactive council.
All in an easy win…..