Representative qualitative research

I was thinking about how to judge the goodness of my qualitative research - see chapter 10 of Miles and Huberman.

Are my informants representative? They are to some extent self-selected in that their organisation's management accepted my approach asking to research them. The management then suggested which IT project or programme to study. In that sense, the informants didn't volunteer, though the organisation did. So informants and organisations may not be representative.

But representative of what? They are representative case studies of successful IT projects, not failures. That's clear because:

1. the organisations made the cases available - I'd assume they'd not make failures so available
2. several of the cases have been submitted for awards
3. the pride is in the words and terms that the informants use

Informants tended to be articulate and elite in management, but outliers were available for interviews at very short notice, such as a clerk, a techie chap and a data input person. So does that mean I've got something representative - both management elite and operational grade informants?

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Miles & Huberman in Miles, M. B. and A. M. Huberman (1994). Qualitative Data Analysis : An Expanded Sourcebook. Thousand Oaks, Sage Publications.