Need help determine the earliest date I can use for my ILR application

[Kunlexzee10]

Hello,
I submitted an application to switch from a Tier 4 dependant visa to a Tier 2 Skilled worker visa on 28/11/2023.
I got the decision and date of issue on my BRP as 22/01/2019.

My questions are
1. which of this date will be legal date to use as my ILR start date calculation.
2. What date is the earliest I can apply?

I have heard some people saying you can start calculation using your date of application.

[Casa]

Hello,
I submitted an application to switch from a Tier 4 dependant visa to a Tier 2 Skilled worker visa on 28/11/2023.
I got the decision and date of issue on my BRP as 22/01/2019.

Correct date

[Kunlexzee10]

Hello,
I submitted an application to switch from a Tier 4 dependant visa to a Tier 2 Skilled worker visa on 28/11/2018.
I got the decision and date of issue on my BRP as 22/01/2019.

My questions are
1. which of this date will be legal date to use as my ILR start date calculation.
2. What date is the earliest I can apply?

I have heard some people saying you can start calculation using your date of application.

[CR001]

1. which of this date will be legal date to use as my ILR start date calculation.

The date your Skilled Worker/Tier 2 visa was issued/valid from.

2. What date is the earliest I can apply?

28 days before 22/01/2024

I have heard some people saying you can start calculation using your date of application.

Not true. They are confusing things. It the date your current visa route is valid from.

[Kunlexzee10]

Thanks for the swift response.
Also can I ask
1. what document will my wife(dependant) need when we do apply together to show subsitence of the marriage.
2. Do I need a letter from all previous employer or just my current employer to prove my annual leave or continuous stay. P.S. I haven't been outside of the UK since the date of issue in 2019.

[zimba]

1. Any document can be used. e.g. bills, payments, agreements, etc. 6 documents, from 3 different sources, covering the last tow years
2. All you need to know about the sponsor letter for Skilled Worker route