Explanation Required: ATA (actual time of arr) and ATD (actual timeof dep)

Here is my definition.

- ATA means Touch Down Time (Wheels On the Ground)
-ATD means Take Off Time (Wheels Off the Ground)

-Chocks Off.. Parking Brake Released.. and Aircraft ready to push back
from Gate
-Chocks On.. Parking Brake Applied.. and Aircraft stopped at Gate

My definition of ATA / ATD is what I see being used in FIDS (Flight
Information Display Systems) in both BKK and HKG Airports.. by the
Civil Aviation Department. And, they use Chocks ON and Chocks OFF as
well.

However, I was told yesterday that, Airlines consider ATA and ATD to
be Chocks On and Chocks Off respectively.

Is this true? Why is that? Why give Chocks On the name ATA.. While
there is a already perfect name for it... which is Chocks On. and same
for ATD.

In my opinion again, ATA should be touch down time.. and Chocks On
should be Chocks On (that is arrived at Gate).

Please explain or give some official reference that conforms with what
I hear yesterday.

Thanks.