Satisfying "Build Orbital Station" Contracts

[Checkers]

Is it possible to fulfill the requirements of a contract for building a space station with a certain amount of fuel, electrical capacity, and/ or space for Kerbals by using a pre-existing space station that partly fulfills the requirements? For example, can I complete a contract requiring me to build a space station with space for 8 Kerbals by adding a Hitchhiker module to a space station (built before accepting the contract) that has space for 4 Kerbals, or would I have to add 8 more spaces for Kerbals? 

[Vanamonde]

Contracts usually specify that they can't be satisfied by an existing launch. I'm not sure about the station-building ones, though, since I turn those down  because they don't fit with my play style. Anyway, read the contract terms and look for that clause. 

[AHHans]

The usual "build a new station" contract are exactly that: build a new station. I.e. one made only from components that were launched after the contract was accepted. You can dock with another craft to refuel if you have some "need so much LF/Ox/Ore/Monoprop" requirements, but you need to undock after that to fulfill the contract.

There are other contracts that explicitly state: "expand [this or that station] to have [space for many more Kerbals / a second cupola / a second lab]".

So from the way you asked your question I guess the answer is: no, you cannot fulfill the contract that way. You can build a new station, that has everything that the contract asks for, and then dock it to your existing station after the contract is completed.

[Checkers]

Thank you both! When you dock or undock two vessels the flight timer in the top left of the screen resets to zero, I figured that the game would recognize the spacecraft as a "new" vessel and therefore consider the vessel as created after the acceptance of the contract.

[Snark]

2 hours ago, Checkers said:

Thank you both! When you dock or undock two vessels the flight timer in the top left of the screen resets to zero, I figured that the game would recognize the spacecraft as a "new" vessel and therefore consider the vessel as created after the acceptance of the contract.

Bear in mind that whenever you dock two craft together, the timestamp of the older one's launch contaminates the newer one's, and that remains even after undocking.

So if you take a contract, and you launch a new station... it's fine to dock it to something else, but only if the other ship was also launched after you accepted the contract.

If you dock it to a ship that had already been launched before you took the contract... sorry, your new ship now counts as an old one, even after undocking, and can no longer satisfy the contract.

So be sure to be careful about this!

[Superfluous J]

13 minutes ago, Snark said:

Bear in mind that whenever you dock two craft together, the timestamp of the older one's launch contaminates the newer one's, and that remains even after undocking.

...but only sometimes. I wish I knew all the rules (or even if there are rules) but I've refuelled enough stations in transit (by docking to ships that were in space long before I accepted the contract) to know these situations exist.

[AHHans]

On 9/16/2019 at 5:59 AM, Snark said:

So if you take a contract, and you launch a new station... it's fine to dock it to something else, but only if the other ship was also launched after you accepted the contract.

As @5thHorseman already said: docking to an "old" station for refueling is O.K. Or at least was O.K. in 1.5.x. Obviously you need to undock after refueling and not keep any parts that were launched before the contract was accepted.