Can this combination mean ‘at least’ as in: λέγεται γε δή, at least, it is said so, or does it mean only it is certainly said so. From what I gather from LS and Denn they mean certainly.
And what does “certainly” mean? It has no unequivocal fixed meaning, and the same goes for Greek particles. Your fundamental error is expecting a precise English equivalent, or any English equivalent at all. Such particles often correspond to a particular intonation in English. Not everything—in fact very little—translates well into English. Rather than asking what they mean it might be better to ask what they contribute to the utterance by way of tone.
λέγεταί γε δή. “At any rate it’s said so” or “Certainly it’s said [but is is true?].” Each or neither of these might be appropriate in context, but each would probably be too heavy. It’s a matter of nuance, and English just doesn’t have the subtlety and delicacy of these darling little particles which take a lifetime to master.
Your best bet is to study Denniston, with a view to learning from him and not carping.