Hello !
You are right guys, discussions of "shall" or "should" about texts which are not mandatory (because not laws or statutory regulations, and in addition coming from another country *) they are childishness, though...
* In a true law (mandatory) of the Government of his most gracious majesty Queen Elizabeth, does "shall" be a requirement in a compagny of Arkansas (USA) ? No!
And more generally if me (poor old and french OSH officer) I say "you must do this to have that good result..." you will certainly hear "you should", because I have no authority over you. By cons if I invite you in my area (French Alps) and if you want tourism advices from me, I certainly will tell you "you should" go in the small village named "La Bérarde" in the heart of the hight mountains * called "Les Ecrins (jewels)", it is quite possible that you obey me (hearing "you shall").
* I practice ski-mountaineering (I don't know the exact name, it's trekking in hight mountains with special skis, but outside of ski stations) and today for example with two friends I have hiked from 1200m of vertical drop (and steep slope) under a radiant sun. It was fantastic but I'm tired !
Thanks for yuo and bye !