User blog comment:B214/Question and Answers 6/@comment-26821288-20161103134718/@comment-29963364-20161104073449

No one's implying that.

It's just that, in the case of Issei & Rias training, we know it happened off-screen because it was directly mentioned by the cast (specifically Issei).

And in the case of Sun Wukong training (consistently) with Issei and Vali, it's only been seen on-screen once, then never seen, mentioned, or implied from that point on. So we don't know for certain or not if Wukong is still personally training those two.

Everything that we "know" happended off-screen has either been mentioned or implied by the cast in the story, leaving any ambiguity up for speculation.