First Day SOTN Stamps - Are They Cto's?

I have several First Day SOTN stamps, off cover, with nice circular FD cancels and am wondering if you would consider them as legitimate collectable stamps or just CTO contrived stamps. I'd scan some but my old scanner isn't compatible with my Windows 10 (&%^&$@!#*$#%^^^&&^&^). Thanks ahead of time for your opinions.

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.

As hy-brasil notes, it's a favor cancel (or a philatelic use, if the FDC actually traveled the mail rather than just being handed back), not CTO. Cancelled to order stamps are sold directly to the philatelic market ("to order") typically at a discount to face value (and by the pallet).

The late Adam K. Bert of Pittsburgh, Pa. produced and sold a great many of these SON first day cancels. Bert died in 2007.