Maybe it's just Devon farmers, but in almost 30 years not one has asked to see anything, not one, they have never heard of DSC1 or 2 (except one for one who did DSC1 for his own benefit ) and in my experience (I have DSC2) they couldn't give a flying fart about qualification's, they just want the deer controlled.
I always have photocopies and proof of insurance in my truck at all times, but as I don't actively look for more ground these days it's pretty pointless.
If anyone contacts me to control their deer I have it, but they are never bothered, they have already checked me out before they contact me.