The luchos represents the Torah which was given on shavuos
Or was it….
(I thought this was going to be your your question) when where mikadeish al pi riyah shavuos could have been on 5, 6 or 7 Sivan. Theres’ machlokes if Matan Torah was on 6 or 7 Sivan.
So According to all 2/3 of the time Shavuos was not on the day of Matan Torah, possibly even occruin 2 days before .