Since I match the second blend surface with the "OnSurface" option (for example, at the 16:53 minute), this is not an issue. Once I achieve the desired tangency, I use the edges of the matched surface to split the target surfaces (21:17 minute and 34:45 minute). This is opposite of what most Rhino users do when they use "Match surface", which has the "OnSurface" option turned off by default. The advantage of using "OnSurface" is that it typically add fewer extra spans and control points to the matched surface. Sometimes, it will not add extra spans and control points at all.
This is fun, but shouldn’t you avoid modeling two edges which meet at a single point at the same tangency due to potential tolerance errors?
Since I match the second blend surface with the "OnSurface" option (for example, at the 16:53 minute), this is not an issue. Once I achieve the desired tangency, I use the edges of the matched surface to split the target surfaces (21:17 minute and 34:45 minute). This is opposite of what most Rhino users do when they use "Match surface", which has the "OnSurface" option turned off by default. The advantage of using "OnSurface" is that it typically add fewer extra spans and control points to the matched surface. Sometimes, it will not add extra spans and control points at all.
I have an issue, can I cut a half of object and mirror to other side?
Yes, you can. Depends on the type of object you want to mirror.