I'm generalising here, for the simple reason that I'm a light fixed wing bod, and I'm sure somebody much more knowledgeable than I about rotaries can answer with specifics on helicopter performance (or airline ops for that matter, but your profile says that you are a helicopter pilot).
In general, the performance in the operators manual is the best available (by which I mean most accurate, not most impressive), produced by a company TP, but flying as near as possible to exactly the flight profile (speeds / heights / handling techniques) shown in the operators manual. This generally does not include any safety factors.
There are generally safety factors available, which are intended to account for variability in handling technique, through-life degredation in engine performance, through-life increase in profile drag (dents, surface finish, etc.) and so on. The should be included in any particular operating manual, company SOP, or in national information - the UK CAA have various AICs for example that are either advisory or mandatory depending upon type of flight. For fixed wing ops, these are primarily related to take-off and landing distances, but other factors do exist.
The precise nature of the factors will vary depending upon the nature of operation. For example, light GA ops do not generally include (in the UK anyhow) proverse factors in determining field performance, whilst heavy ops do, there's also a 1.3 safety factor on TODR which is mandatory for public transport ops, but only discretionary for non PT ops.
G