Date display in browser (label vs ISO)

[atomrab]

We originally displayed the ISO date notation in the period list in the new client, but then we had comments about how this was confusing for people used to dealing with the labels. I'm having the opposite impression with dates expressed in non-Gregorian notation (eg BP) -- it's confusing to have to try to calculate these on the fly, especially when one can't tell at a glance what the present value is. Is it possible to either provide both in the list (side by side, in italics, whatever) or offer a toggle button that lets the user decide whether to show labels or ISO values?

I have a mild preference for the latter but would settle for either.