Not my area usually, so just had a read of SG28.17 you mention. It looks like it’s the language used. You used the word “requires”, with SG28 using words like ‘should’ or ‘need’. I’d suggest one is more prescriptive whilst the other is recommendation. Just flicking through it, and considering the consequences of a failure at a later day. Even if it was not required by SG20, if it wasn’t in line with SG28 as an alternative, then management will have some very serious decisions to justify their actions I think that’s how I’d read it. .