Hi ld1000xx, and thanks for your post and question - it's a good one! I am hopeful others in the community will see your inquiry and share their own anecdotal experiences with us here.
I also have something to contribute. In all my experience, I have seen this only a few times. In each case (and, as I said, it was only a handful), the patient required clinical intervention to help remove this type of inspissated and tenacious mucus. From my professional perspective, you are indeed fortunate to have been able to cough this up and out on your own.
Has this happened often to you? Have you had an opportunity to discuss this further with your physician? Is there anything further you are able to share with us at this time?
Wishing you well,
Leon (site moderator asthma.net)