Anecdotally, I have had two jobs where I provided a very clear start date and subsequently had HR ask if I could start earlier.

One one occasion my new boss would be on vacation for my first 2 weeks and I was asked if I was available to start 3 days early so he could get on-boarding kicked-off and bring me up to speed before he left.

On the other occasion there was a specific (and useful) week-long training for the team they wanted me to attend 2 weeks before the start date I had provided.

I was able (and happy) to accommodate both requests, so it was worthwhile for HR to ask, despite my original availability declaration..

Anecdotally, I have had two jobs where I provided a very clear start date and subsequently had HR ask if I could start earlier.

On one occasion my new boss would be on vacation for my first 2 weeks and I was asked if I was available to start 3 days early so he could get on-boarding kicked-off and bring me up to speed before he left.

On the other occasion there was a specific (and useful) week-long training for the team they wanted me to attend 2 weeks before the start date I had provided.

I was able (and happy) to accommodate both requests, so it was worthwhile for HR to ask, despite my original availability declaration..