thanks for your input hy-brasil

Something to consider. No doubt there are a lot of varieties for these stamps, seems like every single stamp has its own feature when studying them in detail.
Personally I don't have time or sufficient patience for detailed plating studies

, however I enjoy to identify the more obvious/spectacular varieties or errors. So I have put aside a lot of Napoleons and Ceres stamps where "something is going on" - keeping them for later studies - just in case I should happen to get the Yvert specialised some fine day.