Yellow leaves before reblooming

[elbie]

I have about 25 orchids. They are dong well and produce flower spikes regularly. Sometimes more than one spike.
A friend of mine said that she was waiting for her orchid (she has only one) to produce a spike and bloom but one of the bottom leaves had not turned yellow yet. She said that the orchid - a phalaenopsis-didn't bloom until a bottom leaf tuned yellow.
I was surprised because that does not appear to occur with my orchids. Some bottom leaves do turn yellow and fall off but that does not seem to coincide with the production of a flower spike. I seem to get spikes when my orchids start to put out new leaves.
Is there any relationship between the production of the flower spike and a bottom leaf turning yellow?
Thank you in advance.
Elaine