Hi. If I understand you correctly, you are referring to the two kinds of missing data that users find in SPSS.
The first - what you called the "ghost cell", I think - SPSS refers to as "system-missing" (or "sysmis") data. No meaningful value is associated with it (in either the output or the data editor; you just see a dot (".")). This most often happens when a subject provides no data for a given variable.
The second type is called "user missing" data (see the MISSING VALUES command). Here, the subject may have provided data, but the analyst wants it treated as invalid for whatever reason. Most often, data are treated as user-missing when a response or set of responses are not appropriate, or do not apply, to them. For example, a subject responds that they are currently unemployed. Therefore, any variables measuring aspects of their current employment do not apply.
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Rick Marcantonio
Quality Assurance
IBM
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