delegation question

[viet anh]

Is there any error if in file of  my parent domain I declare some record
of my subdomain. my subdomain was delegated.
 I have domain vietanh.com, I delegate domain va.vietanh.com for another
DNS server admin. So in file db.vietanh.com I write:
    va.vietanh.com.        IN    NS     dns.va.vietanh.com
    dns.va.vietanh.com    IN    A      10.0.0.1
is there any error if I  add some record for subdomain of domain
va.vietanh.com in file db.vietanh.com and in file db.va.vietanh.com I
also have these record.

for example:
my db.vietanh.com have records:
    va.vietanh.com        IN            NS        dns.va.vietanh.com
    dns.va.vietanh.com    IN        A            10.0.0.1
    www.va.vietanh.com        IN    CNAME            webhosting.com
    va.vietanh.com.                IN        MX    10        mail.com

And in file db.va.vietanh.com I also have these record

va.vietanh.com        IN            NS        dns.va.vietanh.com
    dns.va.vietanh.com    IN        A            10.0.0.1
    www.va.vietanh.com        IN    CNAME            webhosting.com
    va.vietanh.com.                IN        MX    10        mail.com






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