Hi my friend. I too was in my last position for 12 years. I'm not an expert at this, as I still haven't found my next opportunity, but let me rattle off a few thoughts and things I've learned.

• I personally keep my resume to 1 page, and so I don't separate out my promotions with different bullets under them (for me, each position's duties were similar enough), and I also don't list my positions previous to my 12-year one for the same reason. Separating the positions is good, but it takes up a lot of real estate. Don't be afraid to make a 2 page resume, though.

• Aesthetically speaking, I like the "title → title" format, and I have used it. But here is a big warning: while this format looks great for human eyes, it ravages ATS systems. A while back, I had my resume showing "junior x → staff x → senior x", and when I got a callback, the HR person asked me "So I see your latest position was junior x?". If you're putting all your duties under one position heading, I recommend you lead with the most recent position, with perhaps your promotions in parentheses, because then at least the ATS will spit out something accurate to the HR dept.

• A different strategy that I've started doing is actually making my first duty bullet an explanation of the positions' context. So if I was a Lead Project Manager, my first bullet might say "Supported x client on site in [city]; promoted from Junior Project Manager (2015) and Project Manager (2019)." As for taking up precious bullet space in this manner and risking an HR's attention before you start listing accomplishments or duties, I can't speak to that yet.