Fed provided an explanation around this several weeks back - they have been putting new currency in the market since COVID started, for at least 2 months all they were sending was new currency, no fit currency was being provided from any FRB location. subsequently, they have had periods where they again, by FRB branch, have moved back to new currency only. so, you should have ample new currency with which to provide to grandma. reach out to your local FRB office to see what they are doing currently, new or fit.
at the same time, tell them you want to subscribe to their newsletters which provide details around issues such as this.
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