Nice post Sugar! Well said. I would only add:
However, the strength of the flavoring is actually different and it depends on the manufacturer.
Not only the strength but the actual taste too. Just like McDonald's, Denny's, and Starbucks all sell "Coffee;" they taste NOTHING alike.
For example; TFA, FA, FW, and CAP
all make a flavor called "Vanilla Custard" (Cap actually has a V1 and a V2). Yet none of them taste the same as any of the others. And still other manufacturers make flavors that taste similar to a vanilla custard yet they choose to give them a different name.
and why a lot of us stipulate which manufacturer when we have a recipe on these forums.
Absolutely! Knowing the correct flavor name
AND manufacturer helps us to get a better understanding of the intended strength
AND flavor profile of that ingredient in relationship to the rest of the recipe and the intention of the creator.
Now whether you choose to leave it as is, or adapt it to your own liking, is a whole other matter.
This is why it is always good to check directly with what the manufacturer says to start with.
I would add the following caveat; that some of the more common flavor manufacturers like TFA, CAP, LA, FW, FLV, and others, cater as much (if not more) to the food and beverage markets, as they do to e-liquid makers. So their "recommended" starting percentages
may be relative to food and drink and not e-liquid use. Clarify if you can.