Most 3rd Party AU plugins are normally located in
~/Library/Audio/Plug-Ins/Components
Note: This is the Library in the root of your System drive.. NOT the User Library...
A few 3rd party AU plugins are sometimes located in the same location but in the User Library instead...
However, the plugins that come with Logic (Like EXS24 for example) are actually a part of the Logic App itself and so are not stored in these locations...
The Apple 1.6.0 plugins are being validated properly.
What did you mean by this? What Apple plugins and where did you get that version number from...
Are you saying you cannot find the EXS24 plugin for example when you click on the Instrument slot in a Software instrument Track?
Or..
Are you asking about 3rd party plugins like NI's Kontakt or U-he's Zebra2 that do not come as part of the basic Logic Pro X install.
Sorry, but it's not clear exactly which plugins you are not seeing...
Maybe you could post up a screenshot of your Plugin Manager showing the plugins that are N/A?
Did you successfully download all the additional and essential content via the menu option Download Additional Content?
Does the Download window show everything correctly installed? (ie.. it doesnt say Outdated for example)