The demonization of the ECSS documents is explained on page 29 of the ECSS Introduction Training presentation is shown here below.

The Issue of an ECSS document is represented by a letter.

NOTE:

• Most of the ECSS Standards are now all at “Issue C” and some have already one or more Revisions.
• ECSS Handbooks are at “Issue A”

The complete presentation is available from following link –>Introduction to the ECSS Standardisation System (Level 1)