These were some interesting comments to read and ponder.
Yes the earlier ( Scotti ) are Castello pipes did have a smaller air passage, in the stems. Was that by choice or due to tooling available? Only Carlos or Franco can answer that question. If you look back at many of the older brands you will find that air passage in stems were drilled with smaller air passages.
You might also need to understand that in the early days of Castello, the pipes were machine made in once Franco joined the firm they moved to hand made pipes .. around 1969.
Currently and as far back as I have followed Castello they have always looked to innovate and improve. Shapes have had subtle changes to dramatic changes. Internal "engineering" has been adjusted to what the current client / collector / smokers prefer, thus the larger air passages in the stems.
Unlike a number of other pipe firms, Castello does listen to their retailers suggestions. Maybe not all are accepted, but they are willing to listen.
My last visit to Castello ( 2023 ) was extremely interesting. Instead of a team of five carvers there were eight. One of the original five I met on my 2019 visit had retired, which means four additional employees had been added. I was surprised to see that most of the newer fellows were young. Maybe late 20's in age. Franco explained that these younger team members often have some very good ideas. Some of which get acted upon, some not.
Also something to think about ... on the older Scotti era pipes, you may find some with an open draw. Some say the pipes are inconsistent. However, with a pre smoked pipes you just never know if a previous owner had "adjusted" the pipe to suit their needs.