It's best to be safe than sorry really lol we see vosa a lot at are place as they come in from time to time to look at are tacho equipment as we fit and calibrate them.
For you don't drive it with out a card in and if it's a company vehicle in works time dropping bits to a customers house it's hire and reward.
Make sure the calibration sticker is in date as well! It needs doing every 2 years on a digital so 2 years from the date shown on the sticker