My wife's mid 70's Peugeot UJ10 is exactly the same way even though I don't think the frame was ever used in a 5 speed configuration.

I added new downtube shifters for indexing and I was sort of perplexed about what to do. I ended up leaving the one braze-on in place to hold help hold the clamp up for the new shifters. It doesn't interfere with the cable but it does mean that the shifters are a tad higher than normal. It also looks a little odd.