SQL & PL/SQL

I created one package as

CASE 1:
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create or replace package PACK_DEFAULT is
-- Public procedure declarations
procedure proc_test(p_name varchar2 default 'SCOTT');
procedure proc_test(p_name varchar2 default 'TOM',p_salary number default 1000);

end PACK_DEFAULT;

create or replace package body PACK_DEFAULT is

-- procedure implementations
procedure proc_test (p_name varchar2 default 'SCOTT' )
is
begin
dbms_output.put_line('1st procedure executed ' || p_name);
end;

procedure proc_test (p_name varchar2 default 'TOM' ,p_salary number default 1000)
is
begin
dbms_output.put_line('2nd procedure executed '|| p_name ||'& '||p_salary);
end;

end PACK_DEFAULT;
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when i executed procedure as

begin
-- Call the procedure
pack_default.proc_test();
end;

it gave run-time error
pls-00307:too many declarations of 'PROC_TEST' match this call

If i changed in default parameter of number data-type as

CASE 2:

---------------------------------------------------------------------------------------------------------------
create or replace package PACK_DEFAULT is
-- Public procedure declarations
procedure proc_test(p_name varchar2 default 'SCOTT');
procedure proc_test(p_name varchar2 default 'TOM',p_salary number default '1000');

end PACK_DEFAULT;

create or replace package body PACK_DEFAULT is

-- procedure implementations
procedure proc_test (p_name varchar2 default 'SCOTT' )
is
begin
dbms_output.put_line('1st procedure executed ' || p_name);
end;

procedure proc_test (p_name varchar2 default 'TOM' ,p_salary number default '1000')
is
begin
dbms_output.put_line('2nd procedure executed '|| p_name ||'& '||p_salary);
end;

end PACK_DEFAULT;

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then it executed fine and the out put was
1st procedure executed SCOTT
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I have some doubts kindly clarify

1. why second procedure don't gave any run time error as first ?
2. If oracle internal convert the data type of default parameter in number in second case then why is it not working in case first ?
3. Why the 1st procedure is executed not 2nd procedure in case 2nd?

Thanks in advance