Cda completion letter g-13

Hello.
I wanted to know if anyone has information whether cda is issuing completion letter for completed houses in sector g-13.
One of my friend told me that for g-15 completion letter from cda is a must and without it no transfer can take place.

Surprisingly for g-13 i have heard without issuing it one can buy or sell house in g-13. If this is so how will one know of any violations being made to the construction as anytime in future cda will acquire g-13 and may penalize if any violations are found then.