information_schema.table_privileges

Am not able to understand 2 things about table_privileges and is_grantable.
Can someone please help out with this?

Create a table (acctmast).
Check information_schema.table_privileges - there will not be any records
for this table.
Grant only SELECT permissions to a single user - (dbasr).
A single record appears for this relationship (acctmast  - dbasr).
Apart from the above there are 6 more records - all for the postgres user
for the following (SELECT, DELETE, INSERT, UPDATE, REFERENCES, TRIGGER).

(a) Why do these records appear only when the GRANT statement for the
(acctmast  - dbasr) is executed? They should have been displayed even before
the GRANT was executed for dbasr.
(b) [is_grantable] has a value of "NO".
What is the meaning of this column and value?
The documentation says that "YES if the privilege is grantable, NO if not".
A Record appears in this table only AFTER the privilege has been granted.
So why does "NO" appear in the column?

Cheers!

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