Were steam discharges (as used on April 15th) only installed on only the first three funnels? One survivor (whose name I can't recall but is listed on Pellegrino's website) said that steam only issued from the vents on the first funnel.
Steam escape pipes were installed on all four funnels, and while only those on the first three were connected to the safety valves of boilers beneath them, the escapes on the No.4 funnel were not ornaments. The escape pipes on the fourth funnel were connected to pipes and valves in the engine room that were provided to shunt exhaust steam from the ship's auxiliaries past the condensers and directly to the atmosphere when this machinery was required to operate in the non-condensing mode.
Most typically, the non-condensing mode was switched to when, with the ship placed in dry dock, it was still necessary to continue operating the electric plant, refrigeration, ventilation, fire pumps, etc. (In dry dock, with the sea chests lifted clear of the water, there was no supply of water with which to circulate the condensers, so these were obviously of no use.) Mostly, this was done when the ships were dry-docked for shorter periods -- spot inspections, propeller repairs, etc. During longer stays such as seasonal overhauls and the like, when the entire steam plant was shut down, shoreside utilities replaced the electricity and water pressure generated on board.
If you look at photos of the Olympic and Titanic in dry dock, you will see a plume of steam blowing off of the escapes on the No.4 funnel. The same thing may be seen in photos of other ships as well (the Hulton Getty photos of the Aquitania and other ships dry-docked at Southampton come to mind.)