The regs provide that this form of sign may be varied using a 'permitted expression'.
In this case:
The expressions “Match”, “match”, “Event”, “event”, “Market”, “market”, “Day”, “day”, “On”, “on”, any of those expressions in the plural or the expression “Next” or that expression without a capital letter may be used with any of the expressions permitted by paragraph 1, 2, 3 or 4 as appropriate.
1.—(1) A reference to a time, or to times, of the day may be shown as, or varied to, the following—
(a)a period of time expressed as “7.30 – 9.00 am”, “7 - 9 am”, “7.30 am – 6 pm”, “4 – 7 pm”, “4.00 – 6.30 pm”, “8 pm – 6 am”, “8 pm – 6 am next day” or any other time period and which may include the expression “Midnight”, “M’night”, “Midday” or “Noon” ;
I cannot find any fault with the sign itself.
OP, your choice. IMO, on the evidence so far you do not have a strong case, you would be hoping that the authority could not present evidence to the standard required by the adjudicator on the day that 'event day' notifications were present on the signs you passed.
Alternatively, that they commit a procedural impropriety, again to the standard required by your adjudicator.