I don't know why anybody even bothers to mention what the guidebooks say on this matter. Multiple sources say different things. Even two different volumes of the same series of guidebooks disagree with each other. So who cares?
Don't even bother with other sources. Just look at the manga. Look at was is clearly and obviously
drawn and explained right in front of you. There's your answer. You can flip back to prior chapters and see that Goku's right. Every single confirmed appearance of Super Saiyan 2 is consistently drawn that way: with sparks, and usually within a more "fierce" aura.
Now, keep in mind that "consistency" does not mean "one hundred percent perfect." It means that a trend or pattern is so incredibly coherent that any few instances to the contrary are dismissed as minor anomalies. There is clear "consistency" in how the aura of a Super Saiyan 2 is drawn.
It's like when you go to Burger King. Every now and then, a french fry finds its way into the container along with your onion rings. But the rare occasional presence of a french fry or two in your onion rings does not call into question the entire visual definition of either one. Nobody in their right mind would point to a container of french fries and try to claim that they're actually onion rings despite not looking like onion rings. That'd be completely silly.
Well the way I see it, this is just as silly. Yes, a Super Saiyan 2 is not, technically,
always drawn with the sparks. For one, there's instances where no aura is surrounding them or otherwise visible at all, but I don't think I even have to say that those instances don't count. Other than that, you have those anomalies now and then. But they're scattered among dozens of others, all around them, which are drawn correctly and do not come even close to outweighing the otherwise overwhelming conformity.
You could count the rare instances in the Boo arc where a Super Saiyan 2's aura is drawn without sparks on both hands, compared to the likely hundred-plus instance where they're drawn
with them. That's clear consistency. That
means something. It can't
not mean something.
The guidebooks are conflicted, and the story makes no more or less sense either way. The downright
overwhelmingly consistent art is the tie-breaker. I don't know what else to say at this point but to keep stating what it is. "Obvious."