Leave start dates on visa application query

[ukvis55]

Hi, I received an approval letter for Tier 2 General leave to remain which specifically mentioned my new leave start and end dates. The leave start date mentioned was exactly the next day after my initial leave of tier 2 ended. Say if my initial Tier 2 ended 10th May, this approval letter said my new leave start date is 11th May.
But my BRP card got delayed in printing by over 2 months and it has an issue date which is one and a half month after my official leave start date as per the approval letter.
So, if I were to make another application in the future, say change of sponsor, switch, etc, is the date of my current visa from the start date on my letter? Or the printing issue date of BRP ?

[CR001]

is the date of my current visa from the start date on my letter?

Yes.

Or the printing issue date of BRP ?

No.