if you license ever expires while in the renewal process and they have your paperwork, you can call your local office and get a letter of extension that allows you to continue buying off your old license. This extension is usually good for 6 months or until your new license is issued.
I have not had to deal with this on my C&R FFL, but did have to get one of these extensions when I had my 01 FFL. Still had lots of issues, because a lot of folks thought I was trying to scam them and I always told them if they had questions to call the regional office directly if they didn't believe me
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anyway, glad you got your renewal though. that reminds me i have to renew mine this spring.
JOE