User blog comment:FairyRaven/Fairy Tail Chapter 331: Natsu's Strategy, Review and Commentary/@comment-4829046-20130517150220/@comment-7418318-20130518124107

I think that if f-Lucy brought her keys along they would either have summoned the present spirits (and if present Lucy tried to summon the same spirit, it just wouldn't have worked - much like with Gemini's duplicate keys).

Or they would simply have been unable to "get in touch" with the present spirits and thus not worked at all.

But since she only made a jump of a few days, I think the first theory is more likely.

If they do go 400 years into the past, I wonder how that matter with the spirits turns out then (turned out then? Damn we should invent a new timeform for timetravel)?