Reference letters from individuals and one-time clients

[filmcanada]

This thread concerns Self-Employed program. I need your help.

I am an independent filmmaker and shoot and edit videos for clients, mostly individuals.
Do I need to ask for a reference letter if the clients used my services only once and they are individuals, not companies?

What if I only include invoices, correspondences, photos and final videos as a proof of my experience? What can I else provide as evidences for this?