Telling age on imp labels

[sunreon]

I'm sorting my imps and i've noticed that some of them have a more blue tint to the labels! The black is a blue-tinged black, and the shading around the names is more purple than red.

 

I've also noticed that the fonts sometimes have the faintest difference. Some are a little clearer and bolder, maybe a fraction of a point bigger. (between multiple copies of the same scent)

 

Is this a known way of dating your imps? Is it merely that they were running low on toner when printing those labels?

[Doc Constantine]

Different printers over the years, possibly different toner levels as well.