It's amazing how the subject can wander. Back to the AT-6. I flew them in pilot training and spun them left and right. Remember this was before civilians got their hands on them and did things like put the ELT in the tail cone and fill the baggage compartment before spinning. I found it to be an incredibly consistent airplane during spins and spin recovery. Once stabilized, recovery can seem scary, rotation speed increases during recovery. Given that, if the placard says intentional spins prohibited, don't do them. Are you being paid to be a test pilot? If your airplane does not prohibit them perhaps the placard is missing.