Medicare will back date enrollment to 30 days prior to the receipt of the enrollment application. They do this because you are allowed 30 days to notify Medicare. So for example, if you send in an application today, August 6th, and it's received by the MAC on August 9th, then they will back date the enrollment to July 10th (if that date is what is on the form). If you submit asking for an enrollment date of July 1st, and they receive it on August 10th, they will only go to July 10th, not July 1st.
Yes the provider can see Medicare patients of course knowing that if the application is denied or closed they lose out. Billing must be held until the application is complete.