GL_EXT_packed_pixels

In the glext.h header the following defines exist.
GL_UNSIGNED_BYTE_2_3_3_REV
GL_UNSIGNED_SHORT_5_6_5
GL_UNSIGNED_SHORT_5_6_5_REV
GL_UNSIGNED_SHORT_4_4_4_4_REV
GL_UNSIGNED_SHORT_1_5_5_5_REV
GL_UNSIGNED_INT_8_8_8_8_REV
GL_UNSIGNED_INT_2_10_10_10_REV

But I can’t find them in the GL_EXT_packed_pixels description. Are these part of it (I suppose so, when I use them in my code it works as you could expect) and when I query for this extension can I always use these?