why have the CAA not included a medical status box on either the SRG\1119 or for example on the SRG\1125, the IMC application.
Because the Medical Certificate is a separate condition for the issue or renewal of a licence or rating, and is not actually a condition for taking the test! It is a recent recommendation that examiners do not test candidates without a medical certificate; but CAA staff have been seen to revalidate ratings without valid medicals however, they were not applying to have a rating or licence reissued, and would have been refused such an application.
Maybe you should read
ORS 4 No 816
The use of a Medical Declaration with Pilot Licences other than NPPL when flying
SSEA, SLMG and Microlight Aeroplanes
1) The Civil Aviation Authority (“the CAA”) in exercise of its powers under article 242 of
the Air Navigation Order 2009 (the "Order"), exempts any person who holds a specified
pilot licence from the requirement of article 72(2) of the Order that the privileges of the
licence may not be exercised unless the licence includes an appropriate medical
certificate.
2) In this exemption a specified pilot licence is a pilot licence issued by the CAA, other than
a National Private Pilot’s Licence, which permits the holder to fly single engine piston
aeroplanes (SEP), simple single engine aeroplanes (SSEA), self launching motor gliders
(SLMG) or microlight aeroplanes.
3) This Exemption is subject to the following conditions:
3.1 the licence holder shall not exercise the privileges of the licence in any aircraft other than
a simple single engine aeroplane (SSEA), self launching motor glider (SLMG) or
microlight aeroplane for which an appropriate class rating is held;
3.9 the licence holder has a medical declaration which is:
a) valid in accordance with article 73; or
b) valid in accordance with the following conditions:
i) the holder has signed a statement of belief in the declaration that the holder
meets the medical requirements to fly, having regard to the standards specified
by the CAA in the declaration;
ii) the holder reasonably holds that belief;
iii) aa) the holder has authorised a Medical Adviser acting on behalf of NPLG Ltd to
review the holder’s medical records and countersign the declaration; or
bb) the holder's general practitioner has reviewed the holder's medical records
and the consultant responsible for the holder's clinical care has
countersigned the declaration after discussion with the general practitioner
and a medical adviser acting on behalf of NPLG Ltd;
iv) the countersignatory is satisfied that there is nothing in the pilot’s medical history
which prevents the pilot from meeting the medical standards specified in the
declaration;
Your candidate needs the relevant Medical Declaration and then needs to apply for a SSEA Class rating. SEP cannot be added without a valid Class 2 Medical Certificate. It has been this way for the past 11 years and so far as I can recall was the case under the UK system before that.