I do not have knowledge to contradict Bruno Lowagie on subjects regarding pdf.
He must be right 100% .
But just take a look at the links below . Maybe these may help you . From Bruno's comments I am guessing these may not be 100% accurate or maybe incorrect.
PDF/A Validation
The Apache Preflight library is a Java tool that implements a parser compliant with the ISO-19005 specification (aka PDF/A-1). Check Compliance with PDF/A-1b
https://pdfbox.apache.org/1.8/cookbook/pdfavalidation.html
The 3-Heights™ PDF Validato
The 3-Heights™ PDF Validator safeguards the quality of PDF documents and the processes that create them. Documents are checked for compliance with the ISO standards for PDF and PDF/A documents.
http://www.pdf-tools.com/pdf/pdf-validator-pdfa-validate-iso.aspx
http://www.pdf-tools.com/pdf/Support/FAQ/Article.aspx?name=JNI
FREE PDF/A Validator(Not sure if api exist)
This free online service uses the industry leading PDF/A validator from Solid PDF Tools. Solid PDF Tools can do much more than PDF/A validation
http://www.validatepdfa.com/
JHOVE - JSTOR/Harvard Object Validation Environment
http://sourceforge.net/p/jhove/wiki/Home/
Also please read the below stackoverflow links
.net validation of pdfa file
How can I test a PDF document if it is PDF/A compliant?
http://sourceforge.net/p/jhove/wiki/Home/
http://www.validatepdfa.com/