Do you have a link to both of the songs?
Not promising anything, but I can certainly give you a qualified musicologist's opinion on whether the note combination overlaps between the two tracks can be explained by coincidence.
As far as your chances of succesful legal action I'm pretty certain you're on a hiding to nothing, but at least you might have some backup if the other party ever tries to take action against you.
The thing is, if you prove that your wrote your song before January the 10th, 1989, the other party can still claim they wrote the song in 1988 and it is basically nigh on impossible to disprove this.
Anyhow, that is for lawyers to worry about. I can give you a report on the similiarities between the two songs. To give a very simplistic example of how this might be quantified, the chances of two note intervals in a diatonic major scale and in the ionian mode being the same could be taken as 1 in 7. In practice it will be lower than that since certain notes are more likely to follow certain other notes, for example, some notes more urgently need resolving than others, but correcting for this, if two consecutive notes are the same, three, four, et cetera, the odds can be ascertained using a simple mathematical function.