Assuming that the campaign is showing that it will send to 0 people, it's a little nerve wracking, but I'd ensure that the campaign rules state that someone can only flow through once, and then I'd let it rip for the company Y you want to add today.
Chances are good that it would go out to them, but if not, then the worst thing that happens is you miss a little bit of time getting it out to them, and you could troubleshoot with support as to why it didn't go to them.
Sometimes Marketo doesn't show me exactly what I want to see, but as long as I feel confident with what I've set up (and it sounds like your setup works), then I let it go anyway.
Short of doing this... can you tweak the filter to send to just you, or a seed list -- and do you show up? Maybe you could do a test to yourself or a seed list and then feel confident in adding company Y in.