Geralt begins the game with two moves per attack sequence for any given sword fighting style, and through experience learns more. This is what causes the messages like "2nd attack combo!" and "3rd attack combo!" to appear onscreen, culminating in "Final Attack!". As long the the timing of the mouse clicks is correct, each sequence will be completed unless the opponent does not survive the duration of the volley.
A sequence can be interrupted by poorly timed mouse-clicks, or the sooner than expected demise of an opponent, or by a lucky blow from an opponent which incapacitates Geralt. If the timing of the "swings" is not correct, then the sequence will be interrupted and restarts from the first move. If the timing is optimal, and the opponent survives the full series of blows, then you will see all of the "attack combo" messages, right up to "Final attack!". An attack sequence can also be cut short "in a good way" if Geralt incapacitates his enemy and is granted the chance for a coup de grâce.
The "final attack" is the last move in an attack sequence and depending on how skilled Geralt is in that attack, that could be the third manoeuvre, or the forth, fifth or sixth (yes, some attacks have six moves). Initially these sequences will seem more like isolated moves than a series of moves, but this improves as Geralt's skills improve (as you allocate more talents).
Note that "non-style" weapons (any weapon described as "cannot be used in Witcher fighting style" in the game interface, like the axes, etc.) only have a "first" and "final" attack combinations. As with all weapons, this attack "sequence" starts over again after a "final attack combo".
Basically, your last attack sequence does not change until you "unlock" more levels by allocating more talents to that fighting style.
Towards the end of the game, if you allocate a gold talent on level 5 strong steel, Then your sequence would consist of four different attacks of increasing force one after the other.
Remember that level 4 sword talents are power-up special attacks, and therefore *separate* from the normal attack sequences.
"Final attack!": Damage 12 – 36, Attack +40%, Precise Hit 75%
In addition to being able to do the level 4 power-up move (which uses Endurance) to do a separate special attack that is not chained or linked to your normal swings. The level 4 skills are like the power-up abilities in casting Signs.
The sub-set of enhancements like Patinado II, under the different levels of skill only affect that particular sequence. If you never level a sword skill higher than level 3, it might be worth spending points into the level 3 sub-enhancements as Geralt will repeat that level 3 attack, thus making nice use of those enhancements.