The whole purpose of a wrap document is to take different plans and wrap them into one plan, with one plan year, one plan number, one plan document, one SPD, etc. It seems to defeat the purpose to have benefits with different plan years bundled up into one wrap document.
This is true even if different component benefits have different contract years. The contract year under the insurance policy is not the same as the plan year.
In other words, if you only file one 5500, then you only have one plan, and there should be only one plan year.
Many (though not necessarily all) wrap documents have a cafeteria plan. The plan year of the wrap document will often be the same as the plan year for the cafeteria plan. I've seen it both ways, but usually I see the cafeteria plan and wrap plan have the same plan year.
You need to go back to whomever wrote the wrap document and have them fix it.
The answer, of course, is what did they do last year.