Data Access :: Validation For Length Of The Character Data Types

I Have a table with #Sample like below

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#Sample
id int,
SSN varchar(20),
State varchar(2)
 
Sample Data:

ID SSN STATE
1 999-000-000 AB
2 979-000-000 BC
3 995-000-000 CD
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We used filter logic based on the SSN & State.

We are passing these values through variables like

Declare @State varchar(2)
Declare @SSN varchar(20)

While run time these values are lets suppose @SSN = '999-000-000' & @State='ABC'

Now the Result is displayed with the state data Like 'AB' only.

Output: 1 999-000-000 AB

instead it should give system generated error.

Here I have 2 Questions:
1. Why it is taking 1st 2 Charecters?
2. Why it does not have any system generated for length?

I can do validation with Length function for these 2 variables however if have 100 variables then it should not feasible case. So, what is the reason behind?