I think most of us here leave a head space that is the space left when we pull the wand out of the bottle. So, if we are dealing with still mead is the head space really necessary? Would this space + micro-oxygenation through the cork oxidate much faster long time aged meads? Or is this something we should not concern about?
Yes the head space is important. At the very least, you need the head space to cushion fluid volume expansion & contraction from temp change.