And what makes you think those Slavs along Danube in Hungary and Bulgaria were "general" Slavs? The very same Slavs still call themselves Slovene till this very day and it does not mean Slavs in general at all. Its their national/ethnic/tribal name: Slováci (both in Slovakia and Moravia), Slovenci, Slavónci. Obviously Bulgarians not as they adopted name from nomadic Bulgars.
Nestor use Slovene as "Slavs" in general at last on occasion but he nowhere says it was original name of all Slavs.
But even if it was, since 9th ct. it can not be used as such simply because Slavs by that time split in to various branches and adopted new names (if we suppose those were new). When someone (ancient author) speaks about Czechs, Poles, Rus and then about Slovene in Panonia he clearly does not speak about some unidentified Slavs in general. He speaks about specific Slavs who clearly used name Slovene as their national/ethnic name. And they do till this very day.
So translating old church Slavonic "Slovene" as "Slavs" without considering context is simply wrong.