What I was describing used to be the norm for the older tin roofs that were installed in shorter sheets, so, unlike today, you would see several joins from the ridge to the gutter. If you look at old houses, you can see where there are two sheet ends, maybe one inch of the bottom one showing, where a short sheet has been slipped between the two rusty ends to make it waterproof. Whatever rain seeps through the top rusty layer, runs down the new short piece onto the roof.
You just don't see it around much anymore (not that I have looked lately). I guess a new roof is pretty cheap nowdays and people seem to have more money to renovate.
It was very common in Brisbane 20 or more years ago. I used to know it as "re-sleeving" I think.