The role of lay ministers

In Paul Turner's Blog by Paul Turner

Q: Many thanks for your guidance and expertise.  Our parish is fortunate to have many volunteers to assist as a sacristan, lector, EMHC, musicians and the like.  There are times when one individual insists on taking on multiple roles at Mass.  What document can I use to reference that explains the role of lay ministers in the liturgy and supports that a lay minister should have one role during a specific liturgy?

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A: The USCCB cites GIRM 91 here: https://www.usccb.org/prayer-and-worship/the-mass/ministries-and-roles-within-the-liturgical-assembly-at-mass#:~:text=In%20fact%20it%20goes%20so,of%20service%20at%20Mass%2C%20it