Having difficulty understanding Imm EEA Regs 2006. All help gratefully received.

25 yr old Italian national came to UK in 1995 with mum (also Italian national who has R2R having been here over 5 years etc). At school then worked but went back to Italy to work before 5 yrs up. Further work in UK and Italy but never in UK for 5 year stretch. Fell ill with mental health problems when in Italy and came back to UK to be looked after by mum with whom still staying, still ill and signed off. Didn’t qualify for IB but gets credits. IS refused on grounds no R2R.

If I understand correctly he may have R2R and entitlement to IS because, arguably
1. Reg 8(3) he is extended family through serious ill health
2. Reg 7(3) provided he has a registration cert he is treated as family
3. Reg 16 (5) he can apply for a reg cert…can it be backdated if supported by med certs??
4. Reg 14(2) he has R2R until change of circs
Do I understand correctly?!Could habitual residence be an issue also?