Stall speed depends on so many factors that it can change significantly in a single flight.
Weight, altitude, density altitude, angle of attack etc. are all going to have an effect.
In other words, sure, you might want to confirm it, but you should also give yourself some margin since you don’t ever really know what the stall speed is until you stall.
The angle of attack is not a parameter of the stall speed, it is the cause of the stall (for a given configuration, assuming well below transonic speed). This is why for example, for precise handling you should use an angle-of-attack indicator (a large majority of fighter jets and more generally military aicraft have it).
> you should also give yourself some margin since you don’t ever really know what the stall speed is until you stall
The manufacter speed already take into account the afore-mentioned parameters into account, and the resulting speed is the worst case scenario, if not told otherwise (usually max weight, max forward CG).
One should not fly with an arbitrary speed margin, but instead use well-known speedq (1.3Vs, 1.45Vs, where Vs=stall speed in the given config) depending on the flight phase, and remember well the bank angle limit associated with them.
> The angle of attack is not a parameter of the stall speed, it is the cause of the stall
You're right of course, based on the real definition of angle of attack which is based on relative wind. When people say angle of attack is a parameter of stall speed, they're separating speed from pitch.
This isn't really useful but people seem to struggle with the concept of relative wind, so it's a kind of shorthand.
Also there’s planes that have slats and other devices that effectively change the angle of attack of the wing.
And then there’s planes that direct prop wash over the wing so that the power on stall speed is much lower than power off despite the angle of attack being different.
Your airplane can also be in the "experimental" category, which generally means "homebuilt" so the stall speeds and characteristics can only be determined through test flight. I made the decision to empirically demonstrate stall speeds on the very first flight of my homebuilt, before attempting to land, so I knew for sure what they were.
Weight, altitude, density altitude, angle of attack etc. are all going to have an effect.
In other words, sure, you might want to confirm it, but you should also give yourself some margin since you don’t ever really know what the stall speed is until you stall.