If I have a 10 speed shifter I should expect 9 clicks in the lever, correct?

Just bought an SLX 10 speed shifter (SL- M660) from ebay and it only clicks 8 times.  This to me says it’s a 9 speed?

I don’t need to mount the shifter with rear mech etc to prove this do I?

It might help to put a cable in it and put it under tension, but you’re right about the number of clicks

Yeah, if its at one end or the other, a 9 speed shifter would be able to shift 8 times.

a 10 speed shifter would be able to shift 9 times and so on.

afaik, slx m660 was available in 9 and ten speed versions, although I could be wrong of course.

There was a 9 and 10spd M660 shifter. Sounds like you have the 9 speed one.

Thanks, yeah sounds like I got the 9 speed version

Has it got a little dynasys ‘D’ on it?

No Dyna-sys label on them.  Just Shimano SLX