This helper template calculates periods for Belgian certifications, as stated in the following source:

• [1] - certification until 2006
• [2] - certification from October 2007
• [3] - certification from 2009 (changed on April 2008 [4])
• [5] - certification from July 2018

There is no data for the interim period

It returns:

Returns 0 if the data provided is insufficient