I have an alto and soprano AuLos (plastic), and they are both baroque fingered and standard pitch (A=440). I have an alto and tenor Rottenburgh (wood) and they also are baroque fingered and standard pitch.

All of them play flat (to varying degrees) until I get them "warmed up" with my breath flowing through them. The wooden ones take longer to warm up.

Be sure all the recorder joints (head and foot) are securely pushed together and fully seated. If they are slightly loose or a bit "pulled out" that will make the instruments flat.

Just another $0.02...

V