I'm having a go at the Grade 8 Rachmaninov Elegie Op. 3 No.1.
To me, it seems obvious from looking at the music (lots of big arpeggios in the LH) that you would pedal pretty much throughout, changing when the lower bass note changes. But there is nothing in the actual music to say this - in fact, the first note of each bar (which I think should usually be sounded throughout the bar) is only a quaver as written - here's a version which has the music:
And a much better version played by Rachmaninov himself:
Obviously you can hear the use of the pedal in these, and I can see that it would be messy to write it so that the first LH note of each bar was written out as a minim, but are there any unwritten rules for this type of music such that everyone knows you just use the pedal? For some music, the composer might mark the piece as "sostenuto" or give written instructions for use of the pedal as is the case for Moonlight first movement, but there's nothing actually written here to say use the pedal, and if you were attempting to play it exactly as written, you'd end up changing the pedal every quaver!