Members do not waive their rights to appeal when entering an unconditional guilty plea, but they do waive their right to appeal some> issues. In fact, just like in a finding of guilt by a jury panel or MJ, the appeal will be automatic. But, (and I'm speaking generally) with such a plea, what is reviewable by the appellate court becomes limited, which is why such appeals can be expedited - what is reviewable in a plea of guilty relative to a finding of guilty is much more narrow.
It is likely that to have preserved for appeal Lind's ruling (a pre-trial ruling) with respect to the disallowing of the affirmative defense on the Art. 92 specifications, Lakin would have had to have pleaded "not-guilty". He didn't. As such, it's unlikely he can appeal that particular ruling. He can appeal other rulings made subsequent to his naked plea - like sentencing and the like.
Show me where in article 66 it says that all appeals are limited only to those that have plead “not guilty” and been convicted.
You should know better, the purpose of Article 66 is to protect members of the armed forces from being railroaded in kangeroo courts and or forced to plead guilty through any number of methods of subverting the legal processes.
Does the name Sgt. Lawrence Hutchins III ring a bell, he is perhaps a prefect example of a Service member that was railroaded and released under article 66.