There is a question which is titled:
Now, I am basing this application under the GTV route, but combining the time spent on a Tier 2 general visa (immediately prior to switching into my current GTV). My Tier 2 BRP start date is: 12 September 2019.When did you first enter the UK?
(Required)
This is the date you entered the UK when the period of stay you are basing this application on started.
However, I was in the UK well before that. I switched into Tier 2 visa from the Tier 4 doctorate extension scheme visa (Tier 4 DES) within the UK. After obtaining the T4 DES, I had travelled out of the UK & returned on 22 March 2019 (on the T4 DES). I had switched into T4 DES within the UK in Feb 2019. Prior to that, I was on a Tier 4 student visa that was issued in June 2014 in India, and my very first arrival in the UK would be 29 August 2016 on the T4 student visa.
So, given this information, what would be the correct date to fill in for the above question on the Set (O) form?