Given the 'improved accuracy' rethoric on everyone's website, I'd say that the IT-600 sight gives decent hit probability against moving targets out to 600m as opposed to 300m for the basic PzFSt-III. The BW is clearly talking about operational range, not overall (technical) range. You could surely lob a PzFst rocket one mile away, but hitting anything would be potluck. Same with the Dynarange suit.
I don't know what the new accuracy rating has to be to have the same hit% at 600m as the PzFst-III had at 300m, you can probably figure that out better.
Remember that the system is clearly a clip-on sight, so the overall parameters of the projectile (including range) should probably left unchanged from the PzFst-3T.
Thinking about it, what about giving a decent FC rating to the PsFst-3 IT-600 teams?
I don't know if that is doable, but all in all, that would make at least as much sense as increasing the accuracy.
I'll tell you if I find anything reliable about service of other tandem-HEAT weapons. For starters, you may want to look up the Dutch Defence Ministry website, apparently the winning contender of the SRAT program was something called "PanzerFaust-3T600...
dunno how it turned out eventually. With any chance you'll be able to decipher official Dutch articles better than me!