Spotting/blemishes in general occur on all RCM coins (pre-2018), just more common on bullion. I own some older RCM collectible coins but haven't experienced any spotting (the last time I checked). If you look online on other forums you will see people talk about blemishes on their non-bullion RCM coins. Here's one example from another site that I kept because it was an interesting story if you haven't read it before: 5 kg Silver Here's another (slightly older) thread where they talk about it and show some pictures if you are interested: RCM Milk spots The mint's shield technology doesn't seem to have anyone complaining loudly about it still occurring, but I can't speak for myself.
I think any pure silver proof from ANY mint has the chance of developing spots. look at those beautiful girl Brittianias....they have spots...I'm a betting man, and believe they won't get any, but who knows right? It's all a gamble.
I just got mine in the mail. Wow, is it nice! Very, very nice. I think it is a winner, but who knows right? Time will tell.