"Range" isn't just "how far they'll go", a thrown rock in space will continue going potentially forever.
However effective and usable range is very much a thing, for example you have to take into account the communications time for a round trip a controlled rocket, or the sort of engines it has and if they can be shut down and restarted, which means if you're firing at something a long way off you are going to be fighting:
How far the target can move in that time and how that compares to how you expected them to move, which means:
Does your missile have enough smarts to compensate?
Does your missile have enough "sight" to see that change? (especially active sensors that can and will give it away)
If no to either of those how good are the launch platform sensors and can they get that updated information to the missiles in time.
Then you've got "how soon is your missile seen" which means that the further away you fire from, or the faster your missiles bring up their active sensors the longer the target has in which to spot them and take avoiding action or to use counter measures.
The last thing is, your missile might have a specific maximum speed it can reach which will be affected by the launch platforms bearing relative to the target and if it can give it a boost on it's way, the enemy might be moving at a speed that means even at maximum power your missiles might run out of juice before they can reach attack range.
Space combat with non warp speed engines, and light speed comms is very much about positioning and relative bearings and velocities, you can have a super best ever missile, but if you launch it too soon it could perform worse than a rock thrown closer in or a mine left in the likely path.
One of the best examples of this I've found is the Honor Harrington books, where the author goes in (at times extreme) detail about the performance of the missiles, and key points of multiple story lines are based specifically on the relative performance of different weapon systems and the sort of advantage having even really basic FTL comms can give in fights across something the size of a planetary system, and how even "low tech" systems can beat the higher performance ones if used in a smart manner/if you're willing to lose them in high enough numbers (IE one side has really smart missiles that can go much further and faster under control, the other side counters with much bigger/dirtier counter missiles as they can't hit the incoming ones precisely so decide it's better to get a huge near miss that'll hopefully knock out a couple or at least blind the sensors).
.en.wikipedia.org
