Is the convention you used for a/an in "a (n increasingly long) while back" common?
As soon as I saw it, I wondered how I had ever handled the scenario but nothing came to mind. Perhaps I just ignored it and would have written "a (increasingly long) while back".
I've seen it before, so I can't claim credit for inventing it. Not sure how common it is. Situations where it may be employed are unusual so even if everyone always used that construction when possible, it would be rare.
I don't like that part of my post, on reflection. Complexity to no real purpose, and the words miss the meaning I intended. Obviously it's increasingly long ago. Sloppy writing.
"An (increasingly long) while back" is more grammatically correct because the paranthesis is not a separate sentence; it's part of the grammar structure of the sentence as a whole.
As soon as I saw it, I wondered how I had ever handled the scenario but nothing came to mind. Perhaps I just ignored it and would have written "a (increasingly long) while back".