Restrict COS start date change post visa approval

[neohk]

Hello.
I have put in the visa application just now.
What I want to know is that the HR tells me the start date can be changed on my COS if the work start date needs to be changed.
However, would that not cause confusion when the 30-day visa is given to me?
Suppose the work start date is postponed, then technically I should not be in the country more than 14 days before the new start date, even if the visa clearance states an earlier date as it is based on the old start date?

"Your stay must start no more than 14 days before the start date on your certificate of sponsorship."
Scenario:
Old start date 1/4.
I can enter UK on 18/3 earliest.

Post visa approval
Start date becomes say 14/4
I can enter on 1/4
The 30 day visa still say the clearance starts on 18/3 , I am guessing here.

Do I simply refrain from entering using the visa before 1/4 in the scenario given?

[neohk]

Would it be easier if I ask can start date be changed again when you have applied for the visa, or after the visa is approved?

I only know that you can't change the info on the COS when you have used it.
I think the HR is wrong