Private Life Route: Impact of Historical Overstay on Future ILR under New Rules?

[soniaa010894]

Hi everyone,

I’m helping my cousin with his UK immigration applications and would be grateful for the forum's insights, especially regarding the new rules and his historical issues. I've laid out his full history below for clarity.

Immigration History Summary:

Entered UK: Illegally in Dec 1996 (via an agent, no passport).
First Application (2011): ILR on 14-year basis. Refused due to insufficient evidence of residence and entry.
Discretionary Leave (2011-2014): Granted 3 years DLR based on a relationship with a British partner.
Second Application (2014): Further leave applied for after previous relationship broke down. Refused.
Appeal (2015): Appeal was dismissed. Tribunal found he hadn't lived in UK for 20 years and had an aunt in Pakistan.
Overstaying Period: Appeal rights exhausted 21 March 2016. Became an overstayer until 5 April 2017 (a 380-day gap).
Pivotal 2017 Application: Applied for ILR (10-year) but was 380 days late. ILR was refused, but the application was used to grant him 30 months on the 10-year Private Life route. This was the start of his current settlement path.
Subsequent Grants: Successfully extended his Private Life leave in Feb 2021 and again in June 2023.
Current Status: Legally in the UK on the 10-year Private Life route. His current visa is valid until 27 December 2025.
The Upcoming Applications & Our Concerns:

The Extension (Dec 2025): He will apply for his next (and final) extension before his visa expires in Dec 2025.
The ILR (Based on 10 yrs Lawful Residence): He will be eligible to apply for ILR around April 2027 (10 years from 2017).
Our Specific Questions for the Forum:

The Extension (2025): Given that he has already had two successful extensions on the Private Life route, is this next one likely to be straightforward? Or could the Home Office suddenly decide to refuse based on his historical overstaying (Mar 2016 - Apr 2017) or the dismissed 2015 appeal?
The ILR (27) - This is our main worry: How will the new immigration rules (from 11 Nov 2025) regarding overstaying affect his ILR application?

His 380-day overstay is a clear breach of the new "continuous residence" requirement for settlement.
What are the chances of success arguing "transitional protection" as he was already on the settlement path before the rule change?
What strength does the argument have that the Home Office already "forgave" this overstay when they granted him Private Life leave in 2017?
He has a clean record since 2017, is financially independent, and is preparing for his Life in UK and B1 English tests.

Thank you in advance for any advice or similar experiences you can share. It would be very helpful to know if we should be highly concerned or if this is a manageable hurdle with good legal representation.