A verb for having items appended

I am proofreading a document and the following sentence came up:

Unless the data is appended only, then we can assume the temporal sampling has changed.

What the writer is trying to say, is essentially the following:

Unless the modification made to the data only included appending new data, then we can assume that the temporal sampling has changed.

Is there a verb that I could use to describe the original data set only having data appended to it?

Something along the lines of:

Unless the data is only (suffixed, verb to describe adding data, ???)

The way it was written sounds as though the original data was appended to something else.

I hope that the question is clear. If possible I'd prefer a single word, however the most important thing is that the sentence is clear, so if need be I will simply rephrase it.

Solution 1:

You can re-order the phrase so that unless joins the terms, like this:

We can assume the the temporal sampling has changed, unless the data is only appended to.