When your dealing with a product such as this(i.e. a formulation intended for direct human pulmonary inhalation) there should NEVER be inconsistencies.
#1. The product formulation as well as the process and procedure to generate it should be standardized(i.e. there should be one and only one recipe that is followed and there should be an SOP-standard operating procedure- followed on each batch to ensure lot to lot consistency - this SOP & recipe should NOT change). The initial product prototype should also be tested over and over before a final recipe determination is made. All mathmatical calculations required should be checked, double-checked and triple-checked before one drop of ingredient is poured.
#2. Consistency in ingredients and apparatus MUST be adhered too before each lot is started. In FDA cGMP, new materials are required to be quarantined by the manufacturer until said manufacturer can be certain that they match precisely what the recipe/SOP has previously called for each and every lot. Apparatus used must be accurate and graduated to the correct level of precision required for the intended measurement/process intended. Apparatus must also be prepared/cleaned to the proper level proscribed in the SOP(sterilized if necessary and in this case, considering human pulmonary inhalation, it's necessary). Paperwork documenting each lot's creation process and adherence to SOP should be retained for at least several years.
#3. Each lot, after completion, must be randomly sampled and tested to ensure consistency and potency(Hopefully utilizing some type of accepted analytical testing method, HPLC, GC/MS, etc...). Lot #'s & proper, predetermined expiration dates must be assigned and representative samples of each lot must be retained by manufacturer in case a recall scenario becomes a reality. If, for whatever reason, a lot inconsistency crops up after said lot has been released into the market, a recall must be performed to reduce further possible harm and to determine the cause of the inconsistency.
This is a minimum outline of what each eliquid manufacturer should be following and, as I've stated in the past, the eliquid industry as a whole should start self introducing these standards and self-regulating to ensure they are followed. If not, in the future, some willing government bureaucracy will be more then happy to oversee whatever standards they see fit to enact.
Also for anyone who loved the juice ...Karma is a you know what!
