Besides the flatness issue/non-issue Naniwa's and Nortons have a top layer that just needs to be removed before they start honing their best.. I didn't notice this on my Shapton's but it has been some time since I bought those..
At the Denver meet John brought a new set of Norton's and most of the new guys were amazed at just how much lapping was required to get the 4k/8k flat and that top layer gone...
On the Naniwa's also watch that spot where the sticker was, if you can still see that spot clearly, keep lapping and as noted above WATER is your friend...