The Caffeine Standard provides two data points at 205nm and 273nm. The Holmium Oxide Solution covers 14 absorbance bands in the range of 241nm – 641nm. Hence, you can obtain a calibration curve from these various data points and then extrapolate down to 200nm. 

This is the lowest you would need to go because of the UV cutoff of most typical HPLC solvents is just below this.

HSQ & PQ Kits for HPLC Ordering Information