if it says Deep Cycle, then it's a Deep Cycle, period. If it shows CCA on the case it is either a starting battery, or a "dual purpose" battery, If it does not or if it shows a Reserve Amp rating then it's deep cycle. The name "Marine" on the case may or may not mean anything.
I'm not going to argue with you about it. I've been in the marine business for 15 years and along the way have had access to a lot of information by some pretty knowledgeable people including surveyors and guys who did their Navy service on subs, so think what you like.