It's hard finding the data for previous years, but the scenario you described actually happened in that same year, 2018, during the Azerbaijan Grand Prix.
According to the FIA, these were the best sector times in qualifying:
- Sector 1: Kimi RAIKKONENRaikkonen, 35.283
- Sector 2: Kimi RAIKKONENRaikkonen, 40.704
- Sector 3: Esteban OCONOcon, 25.044
It gives us the combined "perfect lap": 1:41.031
However, the pole sitter was Vettel, with 1:41.498, who, as you can see, had no fastest (purple) sector.
As you may remember, the only reason Raikkonen didn't make the fastest lap that day was his oversteering at T16:
. By the way, you can see in the video that Raikkonen has 2 purple sectors already, the third one belonging to Ocon.