It's not clear how much longer Jeff will be out of action, so we've agreed that I will keep this going until he's back.
To answer your question, smearing of a print occurred with GO, as well as without.
To help isolate the source of this, yesterday Jeff printed the ink separation page on gloss, dried with with a hair dryer, and then gently wiped a q-tip over it and found that only shade 1 smeared. So while it may be possible to smear a print by being careless and wiping a finger over it, this is something different and only affects shade 1.
You'll be reassured to know that carelessly wiping a gloss print pre-GO is not standard practice in this part of the world. To explain how this came about ... When Jeff started printing again on IGFS, he tried to dry it in preparation for GO. It didn't dry any of the usual means - waiting and hair dryers. The print appeared wet to the naked eye. At some point you have to touch it to see what's happening and then it smears. If you manage to put down a GO coat, it still smears.
To help diagnose what was happening he rechecked the linearity. The results are in the initial post and showed that the 100% density point was a lot lighter. As Jeff has printed the purge page the density has darkened, but the smearing, as just described, did not cease. At least not so far.
We'd like to understand what is causing this smearing, but let's suppose for the moment that the root cause was the PK line sitting unused for three months. What is the recommended procedure to prevent this on a printer where both MK and PK carts are used, but one of them less frequently? You often recommend to print weekly, but are you really suggesting that the switch on a 3880 needs to be done weekly? That's 6ml of ink for the round trip each week. Only takes 12-13 weeks to burn through a cart's worth of ink. How often should the switch be done to prevent ink settling in a K line that isn't in active use at the moment?
This is sometimes recommended on this forum, see here.