Can an iphone backup deleted texts while obtaining new dates and times?

I have a bit of a situation here. My significant other and I both have iPhones. I happen to have been using her phone one day and discovered some disturbing texts from an ex of hers. The dates paired with the days of each month matched dates from this year and the thread was placed on "do not disturb". She says that the messages are old, but obtained new dates when she backed up her phone. She says that each set of texts appeared on the different days that she backed up her phone and that's why the dates are different. I also have an iPhone and have backed it up many times and this has never happened to me. Does anyone have an explanation for this or know if this is possible?

As far as I'm aware the dates are retained through backups & don't change. Wouldn't be much of a reliable, data sensitive backup if things like that could happen.

Though I did have an older Nokia phone & something like that did happen, but I would expect improvements to be made between then & now as far as that is concerned.