Changing from a parnership to single member llc and back to partnership

I established an LLC in Colorado in 2010 as a partnership with my wife. She was filing a 1065 until we got divorced in 2019. In 2019 she filed a 1065, and granted me 100% ownership on my Schedule K-1. Her K-1 was marked final (with 0% ending partner shares), mine was not. The 1065 for the LLC was not marked final. I have been filing a Schedule C for 2020-2023 as a single member LLC. Was this handled correctly?

Also, I am considering adding my daughters to the LLC now and was curious about "changing back to a partnership". What is the correct way to do this? I'm concerned about raising any red flags filing a new 1065 since there will be missing "gap years" that I filed a Schedule C instead. Is that not a concern?

Thanks for your help.

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