dx codes: when to change illness date

[KARREN]

(PT services done) new to billing PT services
how often do you need to change the dx on the claims form.  I bill for a NP and MD which they are doing PT services on a few patients.  Each superbill I gets they write the dx's on it:
exampl. 
patient Name=ABC  ins= Medcare pt B  first consult date= 11/17/11  Illness occurence date= 11/17/11 which will print in box=14)  dx given = 723.1,724.1,724.2,729.1,784.0

first dos 11/17/11  CPT CODE 99203, 97530-GP,97012-GP,97032-GP  AND DX= NECK PAIN,MID BACK PAIN, LOW BACK PAIN,MYALGIA .

2nd dos 11/22/11 CPT CODE 99212, 97530-GP,97026-GP AND DX= HEADACHES,SHOULDER PAIN, LOW BACK PAIN, (784.0,719.41,724.2,729.1)

3rd DOS 11/28/11 CPT CODE 99212,97530-GP, 97012-GP, 97026-GP  AND DX= LEG PAIN,HIP PAIN, SIACTICA,NECK PAIN (719.46, 719.5,724.3,723.1)

Question:
WHEN BILLING DOS 11/28/11 Do I change the illness date to 11/28/11 and reflect the new dx codes in box 21 or is it okay to continue biling the initial dx given on the first dos?

4th dos 11/30/11 CPT CODE 99212, 94640 AND DX= ACUTE BRONCHITIS, COUGH, ACUTE SINUSITIS 9466.0,786.2,461.9)

Question:
Should I change the dx when this visit is totally different from PT visit.. like dos 11/30/11
Is it correct on this dos to change the illess date to 11/30/11 and the dx codes in box 21 and link dx accordingly. 

[Michele]

I'm starting at the bottom and working up:

4th question:    If the patient is there for reasons other than the pt you wouldn't include those dx's unless the dr addressed those issues.

1-3:    Even if the dx's change, they are really still addressing the same issue, the patient has back/neck pain that is causing other issues and the provider is performing PT.  I wouldn't change the illness date.  As for the dx's, if you are not a coder you should be billing them with the dx's given to you by the provider.  If you are a coder, you should be reviewing the chart to see what dx's were the primary reason for which services and indicate them as such.