You're absolutely right that the rulebook inplies that the renown tokens are limited, Steve.
However, I'd argue that not giving a bonus for every 7 renown during play is against the spirit of the game. It seems off to me that someone who generates a lot of renown during the first half of the game can get a lot of nice bonuses, but that someone who builds a slower engine and would cash more points in the later half would be excluded from that in case the renown tiles run out.
Any comments from Red Raven would be nice indeed!
In our many tests, running out of renown tokens almost never happened. However, I have since decided it should be an end-game trigger and I will put this in the rulebook for future printings.
If the renown tokens run out, it triggers the last round. Players should keep track of renown points on the track with cubes until the game ends (so they will not gain any more bonuses for reaching 7 renown-- they will just leave the cube on the 7 space).