AssetService System Model returns NULL

Dear All

We are using the Dell AssetService (http://xserv.dell.com/services/assetservice.asmx) to manage the support of the assets of our customer. We query the warranty and systemtype information from the service. Sometimes, mostly on new devices, the field SystemModel and SystemType in the AssetHeaderData displays the value NULL (for example, service tag J2NQ85J). Is this a general issue? Thanks for your help!

Best regards
Mario