PDF/UA

We have a number of dynamically generated PDFs on our site that were created using iText 2.1.7. However, we also have a large number of users that have disabilities and use screen readers, like JAWS, to render our PDFs. We use the setTagged() method to tag the PDFs, but some elements of the PDF appear out of order. Some even become more jumbled after calling setTagged() !
This example was written in answer to the question How can I generate a PDF/UA compatible PDF with iText?
I know that iText can generate tagged PDF documents from scratch, but is it possible to insert alternative text for images in an existing tagged PDF without changing anything else?

Chapter 7: Creating PDF/UA and PDF/A documents

In this chapter, we're going to take a closer look at two sub-standards of ISO 32000. We're going to create PDF/UA files that are compliant with ISO 14289 (Universal Accessibility). We're also going to create PDF/A files that comply with ISO 19005 (archiving, or long-term preservation).

English
I know that iText can generate tagged PDF documents from scratch, but is it possible to insert alternative text for images in an existing tagged PDF without changing anything else?
This example was written in answer to the question How can I generate a PDF/UA compatible PDF with iText?
We have a number of dynamically generated PDFs on our site that were created using iText 2.1.7. However, we also have a large number of users that have disabilities and use screen readers, like JAWS, to render our PDFs. We use the setTagged() method to tag the PDFs, but some elements of the PDF appear out of order. Some even become more jumbled after calling setTagged() !
These are some examples that were written in the context of Chapter 2 of the tutorial ZUGFeRD: The Future of Invoicing . C2E1_SimplePdf creates a simple "Quick brown fox jumps over the lazy dog" PDF with some images, but without any structure. This results in a regular PDF. C2E2_TaggedPdf.java uses the same code as the first example, but now we ask iText to introduce structure. This results in a Tagged PDF. C2E3_PdfA3b.java...