What's more likely, shared risers or separate risers?

What are the odds that the risers in a 3 story/6 unit (2/floor) 1920 building are shared?

My condo association is considering some changes--I'm hoping to narrow the discussion down to what's actually possible before we call a plumber. Background--

About the building:
There are 4 sets of risers on each side of the building (kitchen, laundry, 2 baths).
We share a relatively new hot water heater.

Proposed change: Install separate master shut-off valves for each unit.
When I pointed out that this would require 6 separate water heaters, this was modified to installing separate hot and cold water shut off valves for each unit.
When I mentioned the shared risers, which are obvious in the laundry closet that was added when the building was converted, the response was "we can't assume the original risers are shared."
The discussion has devolved to include other plumbing options based on the possibility that each unit has separate sets of riser pipes.

I'm starting to dread these meetings and email exchanges.

Thank you for any advice.

risers

When pigs fly, plumbers will waste time and material installing separate risers to ANYTHING that has one above the other. Either they do nothing, or they install valves at each unit. If you had separate risers, you would see multiple lines going up the walls from the basement.

Thank you for the quick response. I love your choice of words--I plan to quote you at the next meeting.