Found a solution to the problem of losing one of the headphones. Recently lost my left earbud of Soundsport Free wireless. Someone who lost his right earbud, sold me his left earbud. Simply plugged the both earbuds into the charging case and tried to load the firmware via Computer USB. Found that both buds are synched and solved the problem of losing one of the earbuds.
To test it further, I did have another set of the headphones and charging case. I kept on repeating this R&D and am convinced that simply visit this https://btu.bose.com/ (Bose updater website) and even if the firmware on both buds are up to date, simply click, update. Definitely, we found the solution to the syncing problem.. Effectively, we can say that earbuds are interchangeable.