Unlike the other Headmasters, we don't know exactly what was done to Spike between US #38 (when he just had the helmet) and #39 when he was fully armoured and bonded, but we do know that once he had removed himself from the armour, he could then pretty much instantaneously put those "armor plates" back on, and take them off again, as in #51.

I completely agree with Paulbot about the Senior covers - they're brilliant, and I thought the colouring of #83's made it even better.