Only your overall wound count matters... mostly.
Once you go over 3-harm total, you're unstable and prone to bleeding out. It doesn't matter if you got there 1-harm at a time or 4-harm all at once, you're still unstable. There are actually six total "wound states" your hunter can be in, so let me run them down:
- 0-harm fine. This is as hale and hearty as you could hope to be, in your line of work.
- 1 to 3-harm, moderately wounded. You've taken a few blows, but you can hold it together for now.
- 1 to 2-harm, treated. You've received first aid to help deal with a moderate wound you've taken, but you're not back to perfect yet, and further first aid isn't going to help.
- 4 to 7-harm, severely wounded and unstable. This is going to get worse if you don't do anything.
- 4 to 7-harm, severely wounded but stable. You've been treated and while you haven't recovered, things aren't going to get worse unless you get wounded again.
- 8-harm dead. Things got much, much worse.
The actual size of any individual wound doesn't matter for this, only where it puts you on the scale.
However, you are in a position on that scale based on a fictional event that's caused you to take those wounds, and taking 4-harm all at once is more severe than taking 1-harm until it stacks up to 4. It doesn't absolutely inform anything you need to do to get first aid or stabilize yourself, or the sorts of actions which will worsen your wounds when you're in an unstable condition, but your Keeper can very well expect you to take different and possibly more serious measures to recover from a single 4-harm wound than from a bunch of 1-harm wounds that brought you to 4-harm.