Credibility Rigor

I am doing a qualitative study using videotape data borrowed from a research data bank. So I am not collecting the data.

To ensure credibility I was thinking of prolonged and persistent observation of those participants, peer debriefing, member checks and triangulation.

My concern is with triangulation.  I am aware Denzin (1978) four  option including: convergence of multiple data sources, methodological triangulation, which involves the convergence of data from multiple data collection sources, investigator triangulation, in which multiple researchers are involved in an investigation or researcher-participant corroboration, which has also been referred to as cross-examination.


My question? How can I demonstrate triangulation in my study? I do not see how Denzin ideas will fit with my study. Any other ideas.