I have been contacted by a student who wants to reproduce a figure from a paper of mine in Phil Trans R Soc B (this one, in case it's pertinent) in their thesis. The paper itself is apparently not under a CCAL (I normally choose this option if it is available, but it looks like it wasn't for this one), and I can't find any record of the copyright agreement at the time - the manuscript was submitted about ten years ago.
The journal has a link to the Copyright Clearance Centre for requesting permission for reuse; I ran the form myself and it seems that the student can pay a fee to get permission from the journal to reproduce my figure. That is not my question.
My question is, how to I check whether I transferred copyright for the figure at the time? If I didn't I can presumably just send him the submission version of the figure.
I tried searching the Royal Soc website but it seems surprisingly difficult to find this (which I have noticed before with Elsevier; I think they'd rather we assume they always get the copyright).
Related: How to legally re-use images in paper and still continue to use and distribute them in slides? (but this is about a situation where the copyright transfer status is known).