[ElenaEvgeevnaa]

If you look at scores on the PGA tour for almost any tournament you will see a pro or two that has shot the odd 82 or 85 or something when they are capable of shooting 65, that is pretty much equivalent to what you are talking about, a 20 shot swing. An amateur - even a good one- that is used to scoring in the low to mid 80s or occasionally breaking 80 is going to shoot 100 once in a while or they either aren't being honest or they aren't challenging themselves in any meaningful way by playing new courses or playing a different tee or a different club setup.