In a thread in the Esperanto Forums, I was responding to a poster who was wondering whether he should say Mi legas la libron 'D-ro Jekyll kaj S-ro Hyde, tradukita de ... or tradukitan de ...

I said that I thought I had read in PAG that there was a period (before WWII?) when there was a tendency to drop the akordiĝo en sentences like mi hieraŭ ricevis retmesaĝon titolitan 'Ĉu vi volas riĉiĝi?'..

Later in the day I looked in PAG for the reference, but couldn't find it.