Agano should be aware that there was a fourth Agano-class cruiser since four light cruisers were order under 4th Naval Replenishment Program of 1939. Sakawa was laid down at Sasebo Naval Yard on November 12, 1942, so Agano should be aware of Sakawa's existence. Noshiro should be also aware since Sakawa was launched on April 9, 1944.

Which really opens the can of worm about what is a ship's birthday in KanColle.
Date of death is easy (lets ignore their official "date of death")
Date of birth... which ?

Hmm, if we would compare ship construction to biology, this will be my thought.

When the egg and the sperm met - Date of construction begins (Laid Down).
Inside the womb - Actual days of construction.
Birth - Date of launching.
Days as an infant - Actual days of trial.
Fully developed - Date of commissioning.

(This is purely opinion so don't consider this as a fact.)

Also, just to let you know that Shimakaze's speed trial happened on April 7, 1943, which is several days before her commissioning on May 10, 1943.

And Sakazaki made a comic that showing Shimakaze was talking to her older sister before she was commissioned.