It turns out there was no such guidance and the NL were given incorrect information from the FA (who themselves, you'd think, would have easy access to the government to clarify it!).
Elite sport, in this instance, are teams whose player derive a living from playing football so in theory the NLN and NLS, along with most of the football pyramid, fall under that (I suppose the grey area is whether or not its a liveable income). The National League Premier was slightly different in all of this because there are more FT sides and they're linked to the EFL as well, so they had to protect the two up. That said, their rules and regs state that if the PO's don't happen in the NLP then second place will be promoted so the PO's weren't the be all and end all there.
NL PO's due to be played between July 18th and July 31st, but only if at least four of the six clubs agree to participate (all 18 teams, to my knowledge, have said they will). Those who won't or can't won't be punished for not doing so as they would under a normal season.
So as it stands, Chorley and Fylde are down because of Wealdstone and Kings Lynn being promoted, but Maidenhead and Ebbsfleet, strictly speaking, aren't yet but are likely to be when the PO's go ahead.
I think the NL are sending guidance to the PO Club's outlining costs etc and then leave it to the individual Clubs to decide if they're happy to continue.