20 rolls isn't entirely accurate. The manula says the following

At 20 degrees C:
0% flash use: 67 rolls
50% flash use: 30 rolls
100% flash use: 22 rolls

At -10 degrees C:
0% flash use: 44 rolls
50% flash use: 20 rolls
100% flash use: 15 rolls

I don't intend to use it at such low temperatures and don't use flash very often so according to this I'd expect to get about 35-45 out of it.

I do leave them in when not in use. I didn't think that would make much difference, but I will remove them between films in the future.
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