I've trawled the forum before posting and also been through the numerous threads and links posted in response by other individuals. Unfortunately was not able to find anything related to my case.
I was born in the UK (stayed for about 3 months I believe - have a British birth certificate), brought up outside the country (17 years).
Arrived in the UK in 2003 December on a visitor visa when I was 17 years. Mum made an application at that time that was deemed incomplete.
Overstayed my visa - big time

Was studying and working at the time - doing A-Levels, and Uni. Met my wife (she's British) in college 2005 - got married in 2014. Had 1 child at the time in 2015.
made an FLR FP application via solicitors 2015 (1st application).
Was granted a 2.5 year visa on a 10 year route.
I made a further FLR FP application by myself on the 10 year route and was granted a further 2.5 years which expired on 4th Feb 2021 (2nd application). Made a further application, again by myself and was granted another 2.5 years expiring March 2024 (3rd application).
3 x FLR FP applications.
1st application was made on 21st Oct 2015 but was granted in Feb 2016 -
I'm about to make my 4th FLR FP application - hopefully granted and within this visa I intent to apply for ILR.
Now on to my question - to apply for ILR - does the qualifiying period start from when my first submitted (21st oct 2015) OR from when my leave was granted (11th Feb 2016)
Thanks for taking the time out to read my context.