Thanks @crokkon! ,

Well, it seems that they were not included before the HF20!
I had assumed, wrongly, that the first update was this account-creation delegation.

I have tried to obtain that component of delegated VESTS to see how they would influence the previous results using the information in Account Creation and HF20 Changes by @paulag where these delegations are included for 2018 (Jan- Sep)

I have processed and represented this delegation component to compare it with the main component.

The rectified graph for the Monthly Delegated VESTS shows a certain "offset" that decreases until both graphs converge in 2018-09 when the HF20 is activated.

In the rectified graph for the accumulated delegated VESTS the "displacement" is more clearly perceived.

So, the create_account_with_delegation component affect the figures but due it is relatively smaller values with the main component, its flatter appearance and its trend to zero, would not affect in essence the trends and their variations.