I was in the same boat till I recently ran an ICP test and found out my salinity was at 1.030 when I was testing it at 1.026 with a calibrated refractometer. I plan on using my digital refractometer on a normal basis while testing it against a non digital every once in a while. It's nice not having to guess exactly where that little blue line is at too. I lived just fine with a non digital for 15+ years in the hobby though.
I currently have 3 cal fluids. 2 are older and 1 I bought just last week. All 3 are super close and differ by about .0015 at the most even today. I keep the caps on tight and minimize open air time. I simply avgerage out the 3 when i calibrate. To have all 3 guide me so far astray would blow my mind. To be off that far. One is actually filtered ocean water.
How old was your fluid? What brand and kind? I hope you were not using calibrarion fluid meant for electronic device calibration!