If you are choosing to go with Tamiya's color mixes only, then yes their mix for 20B Deck Blue would be correct for all WWII USN deck blue applications.
However, and it is a big however, Tamiya's color mixes are intended to sell Tamiya paint. Their color selection is not the most accurate. The most accurate source of USN WWII colors is in the White Ensign Models Colourcoat line of enamels. Testor's used to make a line of acrylic naval colors which were based on these paints but they are now out of production. Some may still be available direct from Testors or in some online sources.
If you still intend to mix your colors, then perhaps you should invest in a set of Snyder & Short paint color chips as a standard reference. These are available from White Ensign Models or from shipcamouflage.com. They are paint (not ink) which has been correctly matched to the 1929 Munsell color reference used by the US Navy as the period standard.