It depends on what you consider FDCs to be. I think first day SOTN fall in the category of favor cancels, which some people would consider a technical difference from cto. Your stamps likely (99% chance) come from an FDC. These are done when stamps are oddly placed by a collector or dealer servicing their own covers and may have been done by request. Sometimes large blocks or whole panes have been cancelled with SOTN CDS cancels and might still have full gum. All of these then would have handstamp-type cancels. Machine cancel SOTN stamps come from blocks or plate blocks on FDC.
Here to illustrate the subject; this is not mine, though I do have a few other US first day SOTN stamps.