Hmm. Nohadon lived and died before the Recreance, and Tanavast died after it. Not impossible (see: Kelsier) but he'd have had to find something to stretch his soul so he could stick around as a Cognitive Shadow. He'd also have to have known it was possible, and have had a reason to.
That would be a good reason for Honor not having Splintered further since Tanavast's death, if someone had taken it even partially (ibid.)
(Not to reopen the debate, but my two cents on the Splintering thing: the impression I got from the WoB's was that, no matter how many Splinters the Shard creates, as long as the Vessel is alive, they're a unifying force, something like a hive mind, and the Shard is "whole". Note that Brandon specifically said that Endowment is not considered Splintered, despite routinely creating large numbers of Splinters (although they may rejoin with her-- but that's another topic). Once the Vessel dies, that guiding force is gone and the Splinters all fly apart like the bee ships in Star Trek Beyond. Some of the things the Stormfather says support this too - he changed, or was changed, when Tanavast died. It may be that maintaining this guidance requires the Vessel to retain a certain amount or percentage of the total Investiture. I could be completely off base, but I don't think anybody put forward this interpretation.)