Flashband, yes, a strip covering both sides of the roof where the tiles meet. A house along from us had a new roof & has flashband to cover the two separations. Same as mine was.
When I had a new roof 10 years ago, my neighbour said she wanted a flat tile, just like the house across the road, so I had the same tile, then 10 years later, her daughter decided on a different tile, what could I do then??? My choice was in keeping with all the houses that had a re roof, the Marley Modern, my neighbour is the odd one out.