Yes, can information post 18th June be applied to pre 18th June.
What the data tells us for certain is:
1- by 1815 the 1st grenadiers had a content of men aged under 30. Of the 220 men I collected data on, 10% are over 30.
2- none of the men leaving were over 40
3- average age of those leaving was 26
4- average length of service was 7 years
5-of the men leaving 50% had entered the regiment in september 1813.
The issue is, how reflective of the regiment are these men? Of the men admitted in Septmeber 1813, 15% were over 30. In both sets of data no men over 40 either joined or left the regiment. 5% in 1813 were aged 19, 7% 20. men who entered the guard in the second half of 1813 were in the main aged 24.
On 11th September the 1st Grenadiers had 42 officers and 870men. Of these men I have details of 220, some 25% of the total number of men at that point. The total number of men before 11th September I dont have. Siborne estimates 1500 in the first grenadiers, so around 630men different from June to September 1815.
Further comments welcome.