Prior to 2015 the starts were not allocated. There was also a restaurant about 800 metres from the start, where a pre-start meal was served.
If you'd paid for the meal, you queued for that, had your meal, then joined a queue to get into the all-weather pitch that served as a holding pen at the Gymnasium that was the event headquarters. You went through a gate where they stamped your card with your actual start time, and were formed up on the road in groups of 300 or so. There was a starting group in front of you, and you moved into the start position when they'd gone. It was very stressful, and I had a heart rate of 100 bpm before I even turned a pedal.
For the first section of the ride, there were motorbikes at the front, limiting the pace to 30kph through the urban area. The further behind the motos you were, the worse the accordion effect. This year there isn't an urban area after the start, so I don't know what the roll-out will be like.
In 2015 they adopted the system that LEL used in 2013, with a pre-allocated letter/number start. The three types of card, Vedettes, Touristes and Randonneurs, have one opening/closing time on them, they are not linked to your actual start time, so some mental arithmetic is needed.
The three groups are identified by colour. The vedettes have red numbers and pages in the carnet de route, the Touristes green and the Randonneurs blue.
The specials all started together. I don't know how they organised that, and I did encounter stragglers who had trouble getting to the specials start. It's now completely transparent and rational, which is a bit boring really. The stress in 2015 came from the pre-ride meal running out of the somewhat fussy finger food that the velodrome caterers had laid on. I was already in the velodrome when it was served, and it was obvious that the chicken satay wasn't going to feed the 5,000, as most had three helpings.