Unintentionally, yes. One day I realized I just knew them. The code generator used to hardcode the opcodes, but I have since slowly migrated to use mnemonics, and the opcodes have faded somewhat in my mind.

Of course, I mean the 16 bit opcodes. The SIMD ones, no freakin' way!

It's like the Wizard of Oz. I know most of the dialog, though I never made any attempt to memorize it. A friend of mine knows all the dialog for all the Star Trek TOS episodes. He just realized one day he knew it.