The COAs show peptide purity and volume, but they may also contain particulate impurities and microorganisms like bacteria. Janoshik always filters peptides prior to HPLC analysis, so that analysis is accurate for that vial. But, you aren't using that vial, you are using a different unfiltered one.
Filtering is just another step in the course of harm reduction and one we can take for ourselves. It only takes one nasty ISR or a sinus infection from an unfiltered nasal spray to change your mind. Don't ask me how I know. The odds of induced contamination are low if you follow a hygienic process. Some people never filter, some people always filter. It's a personal choice.
