'gl.getBoundBuffer(target)' lets you query the buffer bound to a specific 
target.

'gl.getBufferStorage(int bufferName)' gives you the GLBufferStorage 
as created via 'gl.glBufferData(..)' or 'gl.glNamedBufferDataEXT(..)',
see GLBufferStorage API documentation!

Further more, GLBufferStorage.getMappedBuffer()
gives you a mapped NIO buffer for that storage as mapped
via 'gl.glMapBufferRange(..)' etc.

Summary:
=========

So what object states do we track currently:
  - object -> target binding
  - GLBufferStorage of object-name w/ storage created
  - GLBufferStorage's mapped NIO buffer

what do we _not_ track:
  - buffer-names which are not bound to target
  - GLBufferStorage of object-name w/o storage created

so one could ask whether a buffer-name has a storage created,
simply by 'null != gl.getBufferStorage(bufferName)', etc.

Bug closed. 

+++++

In GLBase you have:

++++++++++++++++++++++++++

   /**
    * @param target a GL buffer (VBO) target as used in {@link GL#glBindBuffer(int, int)}, ie {@link GL#GL_ELEMENT_ARRAY_BUFFER}, {@link GL#GL_ARRAY_BUFFER}, ..
    * @return the GL buffer name bound to a target via {@link GL#glBindBuffer(int, int)} or 0 if unbound.
    * @see #getBufferStorage(int)
    */
   public int getBoundBuffer(int target);

   /**
    * @param bufferName a GL buffer name, generated with e.g. {@link GL#glGenBuffers(int, int[], int)} and used in {@link GL#glBindBuffer(int, int)}, {@link GL#glBufferData(int, long, java.nio.Buffer, int)} or {@link GL2#glNamedBufferDataEXT(int, long, java.nio.Buffer, int)}.
    * @return the size of the given GL buffer storage, see {@link GLBufferStorage}
    * @see #getBoundBuffer(int)
    */
   public GLBufferStorage getBufferStorage(int bufferName);

++++++++++++++++++++++++++

.. further more, you have:

++++++++++++++++++++++++++

   /**
    * @return true if a VBO is bound to {@link GL#GL_ARRAY_BUFFER} via {@link GL#glBindBuffer(int, int)}, otherwise false
    */
   public boolean isVBOArrayBound();

   /**
    * @return true if a VBO is bound to {@link GL#GL_ELEMENT_ARRAY_BUFFER} via {@link GL#glBindBuffer(int, int)}, otherwise false
    */
   public boolean isVBOElementArrayBound();

++++++++++++++++++++++++++