Re: how much should/does a 17month old talk....
My oldest literally said mama at 17 months, she barely said anything until after age 2. She didnt even babble I was crazy concerned, but she followed directions no problem, so our doc said not to worry, by 2.5 she was saying full clear sentences with a vocabulary that surpassed her peers, and has kept up with that since. My friends used to say it was like talking to a miniature adult. It's almost like she was just soaking up everything all along until it spilled out.
My youngest has been the opposite, so I wouldnt worry about it at all. If she is understanding you she is obtaining.
I know at my youngest 18 month well baby they had a paper that asked if your child knew X amount of words, and it wasnt very high. I think maybe 15.