Applying for new employer from a home country after being worked in China (Issue a new Z visa)

I'm still getting confused with an issue. Is there any problem of applying for a new Chinese employer from your home country after being worked in PRC already? Perhaps you're not getting release letter and cancelation certificate from your current employer (these documents are needed to extend your z type within PRC), and you're leaving your job a bit earlier than the actual expire date of contract & Z type & residence permit, but both parties, me and employer agreed to terminate the contract, so that employer has to somehow cancel foreign expert certificate, residence permit and other important things to make sure that your leave is not gonna get you banned, blacklisted or whatever. Question is, how to ensure that embassy will issue new Z type for a new employer without any problems in my home country, perhaps they might say: "You have to wait till your previous Z type expires, or you need to provide us release letter from your past employer, or you have to cancel your foreign expert certificate... " I'm planning to apply for new employer, as far as i know, if you're applying from a home country, there's no need of possession of release letter. Anyone who knows if there's a phone number in PRC that i can ask such a question directly.. Thank you !