I work on other employees' scribus sla files directly and their versions of scribus vary. We also have an archive of sla files written in older versions of scribus (<= 1.6.1). I noticed some changes in the version 1.7.1, including element names of "ITEXT" and "PAGEOBJECT" changing to "Content" and "PageObject" respectively, and attribute names "CH" and "PTYPE" changing to "Chars" and "PageType" respectively. It might be helpful if a comprehensive list of these changes were made available publicly.
I consulted Copilot regarding the changes, and I attach its response in simplified CSV. I am not confident about the accuracy of the data. Even copilot says the list is not comprehensive. Nevertheless, I hope this is a good starting point.
scribus-sla-token-mapping.csv
Here is a link to my interaction with Copilot. (I'm not actually sure if this would help or whether you would have access to it at all.)