The technology didn't improve. Those implants were recovered from Sleeper outposts in Anoikis (wormhole-space).

Part of what CONCORD enforces is a prohibition on further research into capsule technology. Unfortunately for them, that's as far as their mandate goes, so they can't prohibit the nations from developing immortal soldier technology.

At least, not overtly.

Ok - time to flex my geek brain here and stun you all with my knowledge of Eve lore.... Here we go...

Capsuleer technology was given to the Caldari during the 1st Caldari/Gallente war. But the actual cloning tech was not originally incorporated into the capsules, not only that, becoming a capsuleer was an extraordinarily dangerous process, having your mind linked to a ship was incredibly stressful in the normal human mind. Those who survived, generally could pilot ships in ways that regular crews were simply incapable of doing so, and this ultimately stopped the Gallente advance into the Caldari systems and set the empires pretty much as we know them now.

The cloaning technology had been around for quite a while and the memory transfer technology had also been around for some time, the problem was that taking a snapshot of someone's brain at the moment of death. The process of taking a snap shot of someone's brain is increadibly damaging. Often the imaging system was very unreliable as system had to detect a potential threat and capture the persons mind BEFORE they expired. The number of variables in working out when to take this image in an uncontrolled enviroment regularly meant that system misfired, frazzling the persons brain in the process. Often when the individual wasn't under any real threat at all, and even worryingly, when possibly the system was somewhere where the data could not be transmitted to the new clone. This resulted in people not being revived leaving either a dead original body, or a vegetable with a scrambled brain, or, even worse, the snapshot would be taken too late and the clone would remeber its death and psychologically traumatise it.

So personal cloaning tech was extraordinarily dangerous.

However, combine it with the controlled environment of a capsule, where as soon as its outershell cracked the transfer process would begin meant there was no real margin for error.

But, the mercenary implant works differently, as sleeper technology, it is far in advance of the standard conscious transfer systems employed by the empires at the moment, it is more compact, meaning it can be used as a implant and not something that needs to be carried. According to templar one, it continiously "streams" data to a processing unit, so there is no taking images of the persons mind at the right time, it actively records all the brains activities without destroying its functions.

This means, that as soon as the signal from the current clone body stops being received by the revival unit it can immediately revive another clone using the stored information that had be streamed to the unit prior to the clones death. Then all you have to do is snip the traumatic death bit off the end.

That as I understand it, is the breakthrough of the sleeper implant technology.