Had it not, I presume I could have noted the difference and used the hydrometer by applying the difference to the readings.
Yep, you could have had them test a sample at 35ppt or 1.025 @ 80* and then tested the same with your hydrometer and marked the spot on the hydrometer.
If the refractometer was an ATC
, it would not have any impact (or very little) on the readings for the refractometer, to get a good idea if your hydrometer was off, and how much, you would have needed to take it with you and test the same sample at the same temp.
here is a cool link or two