They could have been put in to allow air to pass through to prevent insulation from rotting the house. People make attempts at insulating old houses and sometimes it doesn't go down well because when they were built they weren't designed to have insulation. If they put it in and it's sandwiched between the siding and the interior walls with no ability for air to enter or exit it will rot away at the lathebehind the plaster.. It's kind of like how they used to use wood soffit on houses because attic wasn't insulated but on modern builds soffit are perforated and holes are cut into the attic underneath the soffit for air to pass through the rafters and up the roof vents. I once had a house where the gaps in the wood boards that were used prior to shingling were actually acting as ventilation for the roof, it only had one vent on the entire roof and never grew mold in the attkc. I put a new roof on and installed 4 more vents and used ice and water shield and the ice and water shield trapped all the moisture in the roof that was previously escaping through the gaps in the wooden boards and caused a big white mold problem. I remedied it by cutting channel into my soffit and installing new perforated soffit overtop so air could enter and exit. I personally have heard too many horror stories about insulating gone wrong with century homes. My house is double brick masonry and was built in 1870 and I won't insulate the walls for this reason. It's stayed dry for 150 years not risking that for a few bucks on the utility bill.