What is "older content" now? Omen/DynaD/Vagary and older, or Ody C and Gaes Fete now too?
New would be sortie + gaol and you will rarely see any shouts for those during EU time.
Omen - not consistent will randomly see a couple of shouts per month. For Omen there will always be people to join you if you ask in social LS's.
Dyna D - for wave 1 clear you will see 2 or 3 shouts per week... for wave 2+3 once every few months. There are still some social LS's that run this every now and then.
Vagary - never see any shouts.
Ody C - daily shouts for casual runs but dont expect more than 5000-8000 segments
Gaol - not consistent. Every now and then you randomly see shouts for V0 - V15. Usually a static trying to replace a missing member.
Gaes Fete - never see any shouts.
Sortie - I usually see 1 or 2 shouts daily for casual sortie but on Bahamut casual means something very different xD. 5-13k-ish gali runs are what you should expect when joining them.
The above is specific for EU time-zone only.