14 days isn't relevant as regards reps, it only affects the discount.
The PCN does not say that unsuccessful reps made no later than the 14-day period would secure the discount for a further 14 days.
Talking of reps, Hippocrates might care to consider weaving this into any appeal or reps:
(8)A penalty charge notice under this section must—
(a)state—
.....
(viii)that the person on whom the notice is served may be entitled to make representations under paragraph 1 of Schedule 1 to this Act;
IMO, this PCN does not and omits vital information. Instead, it invites the recipient to join up dots and reach a conclusion which is improper: it should be absolutely clear.
Schedule 1 to the Act:
Representations against penalty charge notice
1(1)Where it appears to a person on whom a penalty charge notice has been served under section 4 (Penalty charges for road traffic contraventions) of this Act (in this Schedule referred to as “the recipient”) that one or other of the grounds mentioned in sub-paragraph (4) below is satisfied, he may make representations to that effect to the enforcing authority.
....
(3)The enforcing authority may disregard any such representations which are received by them after the end of the period of 28 days beginning with the date on which the penalty charge notice in question was served.
(3) is not in the PCN. Instead they invite the recipient to join up these dots:
From the PCN:
.....
(v)that, if the penalty charge is not paid before the end of the 28 day period, an increased charge may be payable;
(vi)the amount of the increased charge;
Which means what?
That the recipient cannot make reps after the 28-day period as if issuing a CC draws a line under matters? If so, it is non-compliant.
A recipient MUST BE TOLD that they may make reps at any time, but that if made after the 28-day period these MAY be disregarded.
For regular posters, IMO this is a safety net equivalent to an OOT SD or late appeal to the adjudicator i.e reasons for lateness.
There might be 1000 reasons why reps are made late and which, when the reason is presented to the authority, obliges them, by virtue of their public law duty, to act fairly and consider. This doesn't bear upon the substance of reps, but simply the reasons for lateness.
This PCN doesn't convey this info...other than possibly to those steeped in road traffic law(or, in the case of this council, folklore) because it's what we know it's supposed to say and only join up dots leading to this end.