Hi Repairman,
I going through something similar with my new to me '96 850t. Yes, the computer can throw a code even if the readiness monitors are still not set. In my case i installed an R ecu into my 850t and it is throwing a code for EGR sensor... the only problem is that the R ecu is from a '95 that had an EGR and the '96 is not equipped with an EGR so not doing any damage, just setting the pesky cel light. I have my own OBD reader and it shows both the code for the EGR and displays that the monitors are still not in readiness mode(when they blink on and off they are not ready). It can take a bit of driving cycles for these monitors to set themselves...just keep driving.
As to the evap code, my daughters '98 s70 had a similar code. Gas cap was fine on hers. Ended up being a bad emissions hose under the car. look at the "j" shaped hose going to the cannister as well as the hoses leading back from cannister up to the fuel filler inlet. This is where her problem was... a frayed and leaking hose. Replaced with a new one and all has been good. You have to look carefully as it is tight under there. If i remember correctly some of the hose connections where covered with a sheath that needed to be pulled back to inspect. Hope this helps.

Good luck,

Dan