went to shenzen yr 2006. do we still need to present nbi clearance & employment certificate? tnx!

Every application of Chinese Visa is reviewed by its own merits. Even if you have been issued a chinese visa before, you still have to present all requirements stated on the website. Visa officer accepts your visa application as new application regardless of past visa issuance.

If you just got a 5 days Shenzhen visa on arrival in 2006, you will be regarded as a first time China visa application, you must submit additional documents for first time China visa applicants. Only previously used China visa sticker in old or new passport is accepted, those with stamped visas have to submit additional documents for first time China visa applicants.

A single entry is generally valid for 3 months, you should apply for visa in early March if the trip is in April.